ABSTRACTSpore concentration, tube culture age, nutrients, high temperature, and pH were studied to determine their effect on germination ofRhizomucor mieheisporangiospores. Germination was evaluated by incubating the spores for 6 hours at 45 C on a defined glucose-basal agar (aqueous solutions of nutrients were used to evaluate their effect on spore germination). The six spore concentrations tested did not affect the percent spore germination. A sharp drop in the percent spore germination occurred when spores were obtained from cultures incubated at 40 C for more than 10 days. Spores did not germinate in distilled water nor in solutions of KNO3or vitamins. Spores did not germinate after being incubated in distilled water for 5 minutes at 65 C, for 2 hours at 60 C, or for 12 hours at 55 C, but not all of the spores were killed by these treatments. Percent germination was not affected when the pH of the buffered, liquid glucose-basal medium was between 4.5 and 7.