Biochemical and hormonal studies including F.B.S.. HbA1 , s.T3, . s.T4, T3.:T4 ratio . s. AST , s.ALT , s. ALP and s. ACP activity were measured in 100 diabetic patients and 55 control subjects . From these groups 71 diabetics and 20 controls were selected blindly for serum amylase determination . All were subjected to a careful clinical-examination after filling a special clinical case sheet performed to select the clinicaly enthyroid diabetics who are tree from diseases which might interfer with our obtaining results . The patients were classified into insulin dependent diabetes mellitus (type I) group and non insulin dependent diabetes mellitus (type II) group and then each group was subdivided into controlled and uncontrolled types according to their HbA,, level fasting blood samples were used for all groups. None of the control group subjects had elevated activity .of s.AST. s.ALT. s.ALP and s. amylase above the normal range. Five out of the 55 control subjects had increased value of s.T:. over the normal range (9 %) while just one subject had Low -serum level of s.T3 below the normal range (1.8 %) . Both types of diabetic patients had significantly higher HbA1 , and F.B.S. levels in particular the uncontrolled ones . Also both had a significantly reduced mean s.T3 (in particular the uncontrolled type II diabetics) when compared to that of the norma] control group with 5 a negative correlation between HBA level and s.T3. serum T4 was normal in all diabetics and showed no significat variation within the groups . T3:T4 ratio was subnormal in type 11 diabetics and Showed a high significant reduction in the uncontrolled one . Serum AST . ALT and ALP were highly significantly different in diabetic group compared to the controls . The uncontrolled type of diabetes showed higher elevation of these enzyme tnan the controlled one . But no direct clear correlation was found between these enzymes activity and HbAr<:: level . Type I diabetics had a significantly higher s.ACP activity^ in particular the uncontrolled one when compared to the normal control group . Serum araylase activity was subnormal and show more reduction in the well controlled type II diabetics . Moreover . no correlation was found between s. amylase activity and HbAi. .-•: level in type I diabetics but a walk correlation was found in type II diabetics . The results revealed the presence of "Low T3 syndrome" in both diabetic groups and it is possible to use s.T3 and T3:T4 ratio as an indirect parameter for metabolic control of D.M. beside HbA level . Also the results revealed that the uncontrolled D.M. more oftenly had abnormal serum enzyaie levels -than the controlled one , especially in type II than in type I diabetics . The causes of these were attributed to hepatic dysfunction which might have an indirect relation to the adequacy of metabolic control of D.M.