The acute and sublethal toxicity studies of two organophosphate pesticides were carried out against the broiler chicks, Gallus domesticus. On the basis of the computed toxicity factor, phostoxin with a 14 day LC50 values of 0.022 mg/kg was found to be 2 times more toxic than actellic (14 day LC50 of 0.048 mg/kg). The results of the biochemical analysis of the blood samples of the broilers chicks exposed to sublethal doses of phostoxin and actellic over a 49 day period of exposure revealed that there was a significant (P<0.05) increase in the level of glucose from an average of 284.5 mg/dL to 337.9 mg/dL in exposed chicks. Similarly, lactate dehydrogenase (LDH) level also increased significantly (P<0.05) from an average of 867 IU/L in control to 932.5 IU/L in the blood of exposed chicks. The levels of total protein in the blood of exposed chicks however decreased significantly (P<0.05) from an average of 7.07 mg/dL to 2.7 mg/dL in exposed chicks. The histopathology studies showed a high prevalence of hepatic vacuolation and lymphocytosis in the hepatocytes of livers for chicks exposed to sublethal doses of actellic and phostoxin. No visible lesion was however observed in the intestines of the exposed broiler chicks. The chicks exposed to sublethal doses of phostoxin and actellic were observed to gain weight over the period of observation and there was no significant (P>0.05) differences in weights of exposed and control chicks. The implications of these results in the management of poultry farm production and the potential use of glucose, total protein and LDH levels in blood of birds as biomarkers of exposure for organophosphate pesticide residue were discussed.