Experimental tinea versicolor was produced in rabbits and humans with P. 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 wk in 3 of 4 animals. One wk 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. Experimental infections without occlusion were not produced. Spontaneous healing usually occurred.