Six different doses of caffeine were used to study its effect on human spermatozoal motility. The recently developed method for assessment of sperm motility by videomicrography was used to determine the percentage of sperm motility, swimming speed (velocity), percentage of progressive sperm, and progressive swimming speed. In doses of 3 and 6 mM/ml, caffeine significantly increased the percentage of motile sperm, but it had no influence on sperm velocity. In doses greater than 6 mM/ml, caffeine exhibited a slight insignificant stimulation that reversed later into an inhibitory effect on all parameters of sperm motility in a dose of 60 mM/ml. Reaching a dose of 120 mM/ml, caffeine caused complete immobilization of human spermatozoa.