Germination of uredospores of Puccinia recondita was inhibited in the violet, red, and far-red portions of the light spectrum but not in the green and blue-green portions. Light was inhibitory only during the early phases of germination, before germ tubes were one-third the spore length. Light was inhibitory only when uredospores were hydrated before being exposed to light. As the length of the hydration process and the light intensity increased, the germination percentage decreased.