Three fungi Neocallimastix frontalis EB 188, Pirormyces communis DC 193 and Orpinomyces ssp. RW 206, representing the predominant cultures isolated from cattle, were shown to respond to the addition of Aspergillus oryzae fermentation extract (i.e., Amaferm; BioZyme Inc., St. Joseph, Mo.) stimulation. Growth rates, protein and cellulase secretion and fungal mass production were all accelerated in the presence of the extract. Analysis of volatile fatty acids produced by these three species sug gested that extract addition ino creased and altered gas production. Fractionation and preliminary analysis of the components present in the soluble extract, which stimulated the growth of the cellulolytic fungus M. frontalis EB 188, were also attempted. Soluble and filtered, sterilized extract was treated prior to use as a stimulant. Pretreatments included dialysis, ultraviolet irradiation, freeze thaw cycling, boiling, autoclaving, digestion with protease, autodigestion, organic extraction, decolorizing-carbon binding and polyethylene glycol concentration. Boiling, protease treatment, organic extraction, freeze thaw cycling and decolorizing-carbon binding reduced the ability of the extract to stimulate fungal cultures. Gel electrophoresis methods demonstrated that protein- and cellulase-secretion profiles were not identical in control and stimulated cultures. High-performance liquid chromatography methods allowed the separation of the extract into a limited number of ultraviolet-absorbing peaks, of which several stimulated the physiology of the fungus.