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There is evidence that intracellular Ca2+ concentration plays significant roles in sperm function such as motility and acrosome reaction. Many calcium channels have been identified in the plasma membrane of sperm. Progesterone (P4) stimulates Ca2+ influx and acrosome reaction in human spermatozoa. The effects of three multivalent calcium channel blockers, cadmium, lanthanum and nickel on the P4-induced Ca2+ influx and AR in human spermatozoa were determined. Pretreatment with the blockers before P4 challenge decreased the amplitude of the transient of P4- induced Ca2+ influx in a dose dependent manner. Lanthanum was the most potent. The results also suggest that Cd2+ permeates the sperm cell membrane mainly through the same pathways of Ca2+ influx. All three calcium channel blockers significantly (p