The effect of sexual exhaustion on serum testosterone level in bulls was studied. It was found that for all the bulls the serum levels of testosterone after exhaustion trial were more than that before. Statistic al analysis of the obtained results revealed a significant increase only (P/ 0.05) in serum testosterone level after exhaustion in the first trial within the green season. The mean testosterone level for all bulls in the dry season was 3.52 ng/ml before the first trial and 5.04 ng/ml after it, and 3.96 ng/ml before the second trial and 5.29 ng/ml after it. In the green season the mean testosterone level for all bulls studied was 1.72 ng/ml before the first trial and 3.75 ng/ml after it, and 1.77 ng/ml before the second trial and 3.63 ng/ml after it.