Addition of different levels of theophylline (.08.17.25,5 mg/ml) during preservation (4°C) of bull semen in egg yolk citrate medium had a stimula tory effect on sperm motility. It increased the preservation time of bull semen by delaying the loss of sperm motility. Immotile bull sperm due to cold shock could also be mobilized by activity of theophyline. Moreover, theophylline reduced the metabolic activity and increase the resistance of bull semen to 1% Nacl solution.