ABSTRACTLinoleic acid was oxidized by soybean lipoxygenases I and II (LOX‐I and LOX‐II). The monohydroperoxides (HPOD) formed were isolated and then hydrogenated. The mixtures of hydroxystearic acid isomers obtained were converted to phenacylesters and analyzed by HPLC. The isomers were identified on the basis of cochromatography with reference materials and mass spectrometry. It was shown that LOX‐II forms mainly the 9‐and 13‐HPOD (94%) and in addition the 8‐, 10‐, 12‐ and 14‐HPOD as minor components (6%) of the monohydroperoxide fraction. The minor hydroperoxides were absent when the catalyst was LOX‐I. The presence of the poly ene crocin in the reaction system containing LOX‐II changed the composition of the HPOD mixture. The proportion of the 13‐HPOD increased at the expense of both the 9‐HPOD and