Lipoxygenase, prepared from Virginia-type peanuts, was used to catalyze the oxidation of linoleic acid and methyl linoleate to form the C-9 and C-13 hydroperoxides. These reactions were monitored by rapid unconventional direct gas chromatography-mass spectroscopy. An aliquot of the enzymatic reaction mixture, without prior extraction or chemical modification, was secured directly into the heated (40-70 C) or nonheated (room temperature) injection system. When the reaction mixture was analyzed at room temperature, only hexanal was found. At elevated temperatures, five major and several minor components were identified. The predominant compounds identified were pentane, hexanal, 2-pentylfuran, trans-2,cis-4-decadienal, and trans-2,trans-4-decadienal. These products originate from decomposition of either the C-9 or C-13 hydroperoxides generated by peanut lipoxygenase.