The activity of cholinesterase (ChE) in serum, acetylcholinesterase (AChE) in brain,as well as acid phosphatase (ACP), alkaline phosphatase (ALP), aspartate amino transferase (ASAT), and alanin amino transferase (ALAT) in serum and brain of the quail after oral exposure to various single doses of chlorpyrifos (0.1, 0.25, 0.5 and 1.0 LD50) for 24 hours or daily low dose (0.1 LD50) for three months was studied. Results revealed that exposure to the oral single tested doses caused a significant inhibition of both ChE in serum and AChE in brain after 24 hours. The daily exposure to the low dose (0.1 LD50) for three months resulted also in an inhibition of the activity in both serum and brain. The percentage of the inhibition of ChE in the blood serum following the acute poisoning reached about 90% of the control value, while that of AChE in the brain reached about 46%. ACP activities in both serum and brain were also inhibited. Significant decrease in ALP activity was observed in serum while it increased in the brain after acute and subchronic toxicity. In general, ASAT activity was inhibited significantly in the brain. On the other hand, the activity of ASAT in serum after 24 hours of exposure is generally increased while it decreased significantly after daily exposure for one, two, and three months. In contrast, the activity of ALAT increased significantly in both serum and brain. These changes in enzymes activity may reflect liver and / or kidney dysfunction and tissues damage.