(100) mg/kg/day Chloramphenicol was administrated orally to two groups of rats named group (1) and (2) . To group (2) only , an oral acetaminophen was co-administered in a single dose of (50) mg/kg/day . A third group of animals recieved no treatment to serve as a control group. The treatment period for both groups was sixteen consecutive days; samples were taken at 4-day intervals. In both groups serum level of Chloramphenicol was measured two hours after the last single dose administration . The difference between group (1) and group (2) regarding the serum Chloramphenicol and the development of its haematologic consequences was studied . The serum level of Chloramphenicol observed in group (2) is significantly less than that observed in group (1) at days 8 , 12 and 16 and there was a decline observed in group (1) and (2) at day 16 , which was also more marked in the latter group while both groups showed significant reduction in the RBC count at days 12 and 16, the reduction was more marked in group (1) than group(2), but the difference between them was not significant . Significant leucopenia was observed in group (1) at days 12 and 16 ,while group (2) showed a significant reduction in WBC count at day 16 only . Group (1) showed a significant neutropenia with relative symphocytosis at days 8 , 12 and 16 while group (2) showed no significant alterations in the neutrophil and lymphocyte percent. The difference between the two groups was significant at days 8 and 16 . Eosinopenia could be observed in both of the treated groups which was significant at days 4, 8, 12 and 16 in group (1) and only at day 16 in group (2) the difference between the two groups was significant at days 4 . 8 and 12 when group (1) showed a significant decrease in eosinphils from that of group (2) . Significant monocytosis was observed at days 4, 8, 12 and 16 in group (1) and only at day 12 in group (2), the difference between the two groups was significant at days 4, 8, 12 and 16 . Thrombocytopenia was seen in both groups which was significant at days 4,8, 12 and 16 for group (1) and days 8 , 12 and 16 in group (2). At days 4 and 16 group (1) also showed a significant reduction in platelet count from that observed in group (2). Reticulocytopenia was observed to be significant at days 4, 8,12 and 16 in group (1) , and days 4, 8 and 12 in group (2). The significant difference between 'groups (1) and (2) was observed at days 4 and 16,when the reduction in reticulocytes in group (1) was significantly more than that of group (2). A fall in haemoglobin level was observed to be significant at day 16 in group (1) only .Group (1) showed a more pronounced rise in serum iron level with a significant difference from group (2) at days 4 and 12 and from control group at day 12. Bone marrow cell count was reduced in both groups of treated rats . A significant reduction was observed at days 4,8, 12 and 16 in group (1) and at days 4, 8 and 12 in group (2). The difference between groups (1) and (2) was not significant . A rise in myeloid : erythroid ratio (M:E ratio) was seen at days 4, 8, 12 and 16 in group (1) and at days 8 and 12 in group (2) , significant difference could be observed between groups (1) and (2) at days 4 and 16 as M:E ratio was much higher in the former group . Cytoplasmic vaculation was observed earlier and in (25)% of rats in group (1). This type of vaculation was seen in only (5)% of group (2) rats and at a later period of time.