Air sampling using Tenax, a selective solid absorbent, was performed from spawning to pinning over the duration of four mushroom crops of Agaricus bisporus (Lange) Imbach (Fungi; Agricaceae). The contents of the air sampling tubes were thermally desorbed directly to a gas chromatograph-mass selective detector. In two crops 3-octanone and 1-octen3-ol were detected 12 to 13 days after spawning. These two compounds were also detected after compost was added at casing (CAC) and the ketone was present in large quantities. Air sampling of a 10-g sample of spawned compost vs. unspawned compost confirmed that these two compounds were of fungal origin. Bags of spawned compost were used to determine the effects of a CAC layer, a soybean supplement, and Spawn Mate on the volatiles released by the spawned compost. The CAC layer and the soybean supplement selectively absorbed 1-octen-3-ol and, to a lesser extent, 3-octanone. The addition of Spawn Mate to the compost at spawning did not alter the quantity or ratio of 3-octanone to 1-octen-3-ol released by the spawned compost.