Some saprotrophic and ectomycorrhizal fungi produce reproductive structures, preferably in slightly alkaline to neutral forest soil. This research examines the growth of these "ammonia fungi" in liquid medium at various pH values. In the first experiment, the capacity of six buffers was examined to select appropriate buffers for stabilizing pH in the neutral-to-alkaline range by culture of three species of the ammonia fungi in media initially adjusted to pH 7, 8 or 9. The highest buffering capacity was shown in 2-(N-morpholino) ethanesulfonic acid (MES) at pH 7, and N, N-bis (2-hydroxyethyl) glycine (Bicine) and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) at pH 8 and 9. In the second experiment, the growth of 15 strains of both saprotrophic and ectomycorrhizal ammonia fungi was tested on the medium initially adjusted to pH 3, 4, 5, 6 or 7 with MES, or to pH 8 or 9 buffered with Bicine. Many of the saprotrophic species grew well at pH 7 or 8; the ectomycorrhizal species showed optimum growth at pH 5 or 6. The pH suitable for the in vitro growth of these fungi was correlated with the pH of forest soil where these fungi occur.