Rhodotorula minuta cells, which have only traces of carotenoids when grown in the dark, started carotenoid production with the onset of illumination and the amount increased almost linearly until 70 hr then remained constant thereafter when incubation was continued under illumination, with the number of cells continuing to increase. The rate of carotenoid production [Vc (μg g−1 hr−1)] depended on the intensity of light [I(erg cm−2 sec−1)], with the relationship of Vc=0.74 log I−1.46. The final carotenoid content [C(μg g−1)] of cells incubated under continuous light was also controlled by the light intensity [I], with the relationship of C=52 log I−81. Control of carotenoid production by light occurs as a two-phase process consisting of a temperatureindependent photochemical reaction and light-independent biochemical reactions.