The purpose of this investigation was to produce experimental tinea versicolor in rabbits and humans with Pityrosporum orbiculare. Inoculation with P. orbiculare under plastic occlusion on the glabrous follicle-rich inside of the rabbit ear resulted in a tinea versicolor-like lesion after 1 week in 3 of 4 animals. One week after inoculation with P. orbiculare under plastic occlusion, experimental infections similar to those found clinically in tinea versicolor were seen in 10 of 12 patients with a history of tinea versicolor and in 3 of 6 normal volunteers. It was not possible to produce experimental infections without occlusion. Spontaneous healing usually occurred.