Material obtained by the CO2 supercritical fluid extraction (SFE) of the wild and cultivated mushrooms Agaricus silvicola and Agaricus bisporus, respectively, was analyzed by g chromatography (GC)-mass spectrometry and GC-Fourier transform infrared spectrometry. SFE gave results comparable with classical extraction techniques for free fatty acids and esters but with fewer manipulative steps and also resulted in the characterization of acids not previously reported from these sources. The organic acids identified included all of the C5-C26 saturated fatty acids, with palmitic and stearic acid predominating, the C-15-C22 fatty acid methyl esters, and the C4-C-11 alpha,omega-dicarboxylic acids. Benzoic acid was a major constituent in the A. silvicola extract but was only a minor constituent in that from A. bisporus. Only the C-8-C20 monocarboxylic saturated fatty acids had been previously identified from these species. Unsaturated fatty acids were virtually absent, with only minor amounts of hexadecenoic and octadecenoic acids observed.