Abstract: An unidentified species of Diderma, new to Tanzania, is discussed and illustrated. A scanty specimen developed in a moist chamber culture prepared from bark of living Juniperus procera. This moist chamber was cultured for the first time in June 1989 and produced then no Diderma species after one month of incubation. The dried petri dish was stored for ten years in a closed, dark laboratory cupboard and was rewetted in May 1999. After 60 days of incubation an interesting Didermaspecies developed with walnut-shaped spores bearing an equatorial ring or two perpendicular rings. This specimen may represent a new species, but also seems to have affinity to Diderma punense. We have not been able to obtain the type specimen of the latter species from India to compare it to our specimen. For comparison, some specimens of Diderma cor-rubrum with similar spore morphology were studied with SEM.