The effect of light on calcium transport in mammalian sperm mitochondria and plasma membrane was studied. Digitonin treated bovine spermatozoa and plasma membrane vesicles were irradiated with a He-Ne laser and a 780 nm diode laser at various intensities and energy doses and Ca 2+ uptake was measured by the filtration method. It was found that there is an accelerated Ca 2+ uptake by the mitochondria after low He-Ne light and inhibition after high intensity irradiation. The ATP-dependent Ca 2+ uptake by the sperm plasma membrane vesicles was not changed due to He-Ne irradiation. It was enhanced due to 780 nm irradiation.