Piptocephalis virginiana, an obligate parasite attacking only other Mucorales was studied at West Virginia University. Spores of the parasite germinated readily on many natural media. Good germination was also obtained on synthetic media containing glutamic acid. When glutamic acid was autoclaved separately and added later, the medium did not support germination. The parasite attacked certain hosts at temperatures ranging from 15[degree] to 25[degree]C. Helicostylum sp. was susceptible at 15[degree] and 20[degree]C, but resistant at 25[degree]C. Thamnidium elegans was susceptible at 25[degree], but resistant at 15[degree] and 20[degree]C. The parasite strongly inhibited the growth of Mycotypha microspora on glucose-glutamic acid media. Such inhibition could not be demonstrated for other hosts or on other media. Young hyphae of Helicostylum sp. were readily attacked by the parasite, but mature hyphae were very resistant. Varying C and N sources and the concentrations and proportions of the C and N sources greatly influenced the growth of the parasite, often when host growth was not affected.