Unmated (+) and (-) strains of all 4 available spp. of Choanephora and Blakeslea were studied in respect to such growth and sporulation factors as nitrogen sources, carbon sources, carbon-nitrogen ratios, temperature, light, and the influence of other organisms. With glucose as the carbon source, ammonium sulfate and asparagine were the best of 5 sources of nitrogen tested. When asparagine served as the nitrogen source, glucose and cellobiose were the best of 17 carbon compounds tested. Carbon-nitrogen-ratio requirements differed among species. Cultures generally sporulated best at temperatures of 25-28[degree] C and under alternating periods of light and darkness. Sporulation was not generally enhanced by the presence of other microorganisms. Some of the natural variants selected from plate cultures of B. trispora and C. circinans still retained their individuality after 7 transfers over a period of 18 months.