The effects of temperature on storage and viability of asexual spores of Rhizomucor pusillus (Lindt) Schipper and Rhizomucor miehei (Cooney and Emerson) Schipper were studied. An optimal germination temperature of 35 degrees C was recorded for both species with good results obtained around 40 degrees C. On prolonged storage of the spores at various temperatures (-19 degrees C, 4 degrees C, 30 degrees C, 37 degrees C), the best results were obtained at 4 degrees C and 30 degrees C. Very rapid losses in viability of the spores of both fungi occurred at -19 degrees C reaching a maximum of 68% and 51%, respectively, for R. pusillus and R. miehei after 6 months of storage. Continuous exposure of the spores to 68 degrees C led to rapid losses of viability of up to 100% for those of R. pusillus after 40 min exposure. Sporangiospores of R. miehei showed more gradual losses on exposure to 68 degrees C. The potential health hazards which the presence of these fungi on tobacco products pose to man are discussed.