Besides the well known products of lipid peroxidation, 4-hydroxy-2-nonenal, saturated and unsaturated aldehydes, 2-hydroxy-heptanal was found to be a major aldehydic product of lipid peroxidation (LPO) of n-6 fatty acids (linoleic acid 18:2, arachidonic acid 20:4). 2-Hydroxyhexanal is produced also, but only in much lower yield. 2-Hydroxyalkanales with 8,9,10 and 11 C-atoms are derived from hydroperoxides of oleic acid. An oxidation product of all unsaturated fatty acids is glyoxal. Analyses were performed after aldehyde specific derivatization reactions by GC-MS.