The effect of light on calcium transport in mammalian sperm mitrochondria and plasma membrane was studied. Digitonine-treated spermatozoa and plasma membrane vesicles were irradiated with an HeNe laser at various powers and energy doses and Ca2+ uptake was measured by the filtration method. It was found that there is an accelerated Ca2+ uptake by the mitochondria after low power HeNe irradiation and inhibition after high power. The Bur of Ca2+ from the mitochondria was also examined and was found to be unaffected by the HeNe light. The ATP-dependent Ca2+ uptake by the bovine plasma membrane vesicles was not changed by the HeNe irradiation.