Albino mice of different inbred strains have been exposed to constant fluorescent lighting at an illuminance level of 115-130 ft-c for intervals of 1-6 weeks. Under these conditions the photoreceptors in retinas of albino BALB/cByJ mice rapidly degenerate, whereas the photoreceptors in retinas of albino C57BL/6J-c2J mice are remarkably more resistant to light damage. F1 heterozygotes produced from these two strains display an intermediate degree of light-induced degeneration. These findings demonstrate that phenotypically identical populations with different genetic constitutions can show markedly different sensitivities to light, and that genetic factors must now be included as a determinant for the severity of light damage.