Lead (Pb2+) is a toxic heavy metal which interferes with several physiological processes regulated by Ca2+, including those characterized by changes of the membrane stability and the motility of spermatozoa necessary for the fertilization of the oocyte. In this study, ejaculated sperm from six rams (Ovis aries) have been incubated in vitro with or without 50 ng Pb2+/ml during 30 min and in the presence or absence of three different potential modulators of the effects of Pb2+ on changes in the sperm membrane before fertilization: charybdotoxin, quinacrine and staurosporine. Sperm samples incubated with Pb2+ have shown significant reductions in acrosome integrity and sperm viability and an increase in progressive movement. None of the studied potential modulators had a protective effect against Pb2+ action. On the contrary, Pb2+-incubated sperm in the presence of staurosporine had lower acrosome integrity, and lower sperm viability was observed when spermatozoa were incubated with Pb2+ + charybdotoxin. Quinacrine was the only tested substance capable of increasing the concentration of Pb2+ in spermatozoa; thus, the enhancement of Pb2+ effects produced by staurosporine and charybdotoxin was not produced by an increased uptake of Pb2+ by spermatozoa. However, the increase of intracellular Pb2+ in those spermatozoa incubated with quinacrine did not result in an adverse effect on sperm motility or viability although the acrosome integrity was negatively affected.