The present study was conducted to evaluate the acute and subchronic effect of chlorpyrifos on some biochemical parameters in the blood serum of exposed quail. The results illustrated that exposure to sublethal single doses (0.1, 0.25, 0.5 and 1.0 LD₅₀) for 24 hours lead to an elevation of haemoglobin, ammonia and glucose (to some extent), while bilirubin, cholesterol, phospholipids, urea N and uric acid content decreased. In contrast, total protein and creatinine showed an irregular trends. Inorganic P was significantly increased at the highest dose (LD₅₀ value) while triglycerides content increased significantly only in case of administration of the lowest dose (0.1 LD₅₀). Concerning the effect of daily administration of the low sublethal dose (0.1 LD₅₀) for 3 months, it was found that haemoglobin, ammonia, total protein and triglycrides increased, while bilirubin decreased in the treated birds during the whole period of the experiment. On the other hand, cholesterol, phospholipids, creatinine and uric acid did not change significantly. The results indicated also that glucose, inorganic P, urea – N changed irregularly. These changes in the blood constituents may be explained on the basis of liver and / or kidney dysfunction, tissues damage in addition to enhancement or inhibition of the activity of some regulating enzymes.