OBJECTIVE The present study investigates the effect of oral administration of chlorpyrifos (CPF) in indigenous chicken. METHODS The birds were divided into two groups I and II. Group I served as control and group II was treated with CPF (0.36 mg/kg) orally daily up to 12 weeks. Blood samples were assayed for hemoglobin (Hb), total erythrocyte count (TEC), total leukocyte count (TLC), differential leukocyte count, and biochemical constituents like alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), cholinesterase (CHE), total protein and uric acid. Representative pieces of tissues from liver and kidney were collected weekly for histopathological examination. RESULTS A significant (P < 0.01) increase of Hb, TEC, TLC, and heterophil percent and decrease of lymphocyte percent was observed. Serum ALP, AST, ALT, and uric acid increased significantly and CHE values decreased significantly in CPF treated birds. The protein level remained similar. Uric acid level was found to be increased significantly in the treated group. The results indicate that chronic CPF intoxication produces hematological, biochemical, and pathological changes in treated birds.