From February 2000 to October 2000, pleural and peritoneal effusion fluids were collected from 94 patients attending the university hospital of Saddam College of Medicine. Simultaneous blood samples were also taken from those patients enrolled in the current study. Whether fluid accumulation in the body cavities (pleural & peritoneal) is a transudate or an exudate is determined by different parameters, such distinction is important for limiting the extent of the differential diagnosis of possible causes for this condition. So pleural and peritoneal effusion fluids were subjected to various biochemical, immunological and tumor markers and cytological studies. I-Pleural Effusions: A total of 66 patients with pleural effusions were included in this study. They were grouped into three categories according to etiology: - Group one: Included 12 patients with transudate effusions. - Group two: Included 31 patients with inflammatory exudates-effusions. - Group three: Included 23 patients with neoplastic effusions. Biochemical examination of these effusion fluids revealed the following: pleural fluid lactate dehydrogenase (PFLD) activity and a protein concentrations was significantly higher in exudates (inflammatory & - neoplastic) than that intransudates (P<0.05). PF to serum LD ratio was significantly different between transudates and exudates (P<0.01). However, total PFLD activity is of little value in the discrimination between inflammatory exudates and neoplastic effusions, LD isoenzymes activity analysis revealed that PFLD3 activity was higher in inflammatory exudates than that in neoplastic effusions, although it was significant only in- female patients (P<0.01). Moreover, LD3 in pleural effusion fluids and serum have' distinct pattern in the three groups. Adenosine deaminase (ADA) as immunological marker in PF and serum was measured to evaluate its diagnostic utility in tuberculous (TB) pleural effusions. The sensitivity, specificity and diagnostic efficiency in diagnosing TB effusions were 83%, 70% and 74%, respectively. Results indicate that PF ADA is not always reliable for differentiation of TB from other non TB effusions since 42% of cases with neoplastic effusions and non TB inflammatory exudates had a high value of ADA. The use of tumor associated antigens (tumor markers), carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA 19-9) and alpha fetoprotein (AFP) in the diagnosis of malignant pleural effusions revealed the following: levels were significantly higher in neoplastic effusion fluids compared to that in benign effusions (transudates and inflammatory exudates) (PO.05). At cutoff level of 9 ng/ml, 17 U/ml, and 14 lu/ml, respectively, CEA, CA 19-9, and AFP assays discriminated between benign and neoplastic effusions with (a sensitivity, specificity, and accuracy) of (61%, 84%, 76%); (39%, 81%, 67%) and (89%, 66%, 74%), respectively. The analysis of paired serum and PF CEA, CA 19-9 and AFP levels showed non significant between them, but a positive significant correlation between them in all of the three tumor markers (P<0.01). The parallel quantitation of CEA and CA 19-9 in PF could not improve the sensitivity in the detection of neoplastic effusions and showed that these are dependent antigens. Another aspect of the study is to investigate and evaluate the diagnosis accuracy of PF cytology in neoplastic effusions. The sensitivity of the cytological examination was 61% with no false positive results, giving a specificity of 100% and the diagnostic accuracy was 86%. However, 39% of false negative results were observed. The sensitivity increased to 78%, 87%, and 95%, respectively .When cytology and effusion fluid CA 19-9, CEA, and AFP assays were used in adjunction in the diagnosis of neoplastic effusions. II-Peritoneal Effusions: A total of 28 patients with peritoneal effusions were included in this study. They were grouped into three categories according to etiology: - Group one: Included 9 patients with transudative effusions. - Group two: Included 11 patients with TB peritonitis. - Group three: Included 8 patients with neoplastic effusions. The results of biochemical examinations revealed the following: ascitic fluid total protein (AFTP) concentration was significantly lower in transudates than that in exudates (TB & neoplastic effusions), with an accuracy of 89% in separating between transudates and exudates. While serum ascites albumin gradient was more effective, in separating exudates from transudates, than AFTP with an accuracy of 93%. Regarding LD activity in ascitic fluid (AF), was significantly higher in exudates compared to that in transudates (P<0.05). However, it could not separate between TB and neoplastic effusions. Similar to total LD activity, estimation of AFLD isoenzymes activity could distinguish between transudates and exudates but not between various types of exudative effusions. AF LD isoenzymes activity estimation was useful in separating transudates from TB effusions, since the latter have significantly higher AF LD3, LD4 activity than that in transudates (PO.01). Whereas neoplastic effusions have significantly higher AF LD4 and LD5 activity than that in transudates (P<0.01). Moreover, the study showed different isoenzymes pattern between AF and serum for transudates and exudates. The diagnostic utility of ADA in TB peritoneal effusions was evaluated. AF ADA level in tuberculosis group was significantly higher than that in other two groups (PO.001). The sensitivity, specificity, and accuracy of ADA in the diagnosis of TB effusions were 45%, 100%, and 79%, respectively. The level of ADA in AF was significantly higher than that in serum (P<0.05), giving a high fluid to serum ratio in TB effusions compared to the other two groups. Therefore, based on its high specificity, ADA estimation in patients with TB effusions might help in early diagnosis of these patients. Quantitative estimation of tumor markers in peritoneal effusion fluids showed that CA 19-9 assay was specific and sensitive enough to become a valuable tools in the diagnosis of neoplastic effusions. The sensitivity, specificity, and accuracy in the detection of neoplastic effusions was 100%. CEA assay has a lower sensitivity (50%), specificity (90%) and accuracy (78%) in the detection of neoplastic effusions. Whereas AFP assay was of no clinical value for diagnosing neoplastic effusions. The parallel quantitation of CEA and CA 19-9 in AF had a higher ' sensitivity (100%) compared to CEA assay alone. The analysis of paired serum and AF CEA, CA 19-9 levels showed a non significant differences between them. The levels of CEA in AF correlated well with serum level, whereas no significant correlation between AF and serum CA 19-9 levels was found. Cytological examination alone detected malignant cells with a sensitivity of 62% with no false positive results, giving a specificity of 100% and a diagnostic accuracy of 89%. Combinations of cytological examination, effusion fluid tumor marker determination, improved the detection rate of malignancy. The sensitivity increased to 100% when cytology and peritoneal effusion fluid CA 19-9 assay were used in adjunction for the diagnosis of neoplastic el fusions. Whereas a lower sensitivity (87%) was found when CEA assay was used in adjunction to cytology. It is suggested that CEA, CA 19-9 assays provide a useful adjunct to cytology for the diagnosis of malignant peritoneal effusions.