AbstractMonohydroxy derivatives of polyunsaturated fatty acids such a s arachidonic acid (AA) and linoleic acid (LA) can inodulate inflamation and epidermal proliferation. The purpose o f this study was to determine thein vitodistribution orthc AA derivatives; 12‐ and 15‐hydroxy‐ eicosatetraenoic acid (1 2‐HETE and 15‐HETE) and the LA derivatives; 9‐ and 13‐liydroxyotadecadienoic acid (9‐IHODE and 13‐HODE) in specific phospholipids of normal humoii skin. Lipids were extracted from 6 normal keratoine skin biopsies and phospholipids were separated into the major classes by two‐dimensional thin layer chroiiiatograpliy. Monohydroxy fatty acids (MHFAs) released from specific phospholipids after treatment with phospholipase A2were identified by reversed phase and straight phase high‐performance liquid chromatography and UV‐absorption spec‐ tra. Unesterified MIHFAs were deteriiiined in a similar way. 9‐MODE, 13‐HODE and 15‐IHETE were detectable in pliospliatidylcholamine (PC), pliospliatidylinositol (PI) and pliosphatidylethanolamine (PE). Interestingly. 12‐NETE was not detectable in these phospholipids, although the Linesteriried 12‐HETE was detectable in amounts similar to uncstcrilied 15‐HETE. Eskrilied I 5‐HETE was equally distributed between PI arid PC, in which IS‐HETE was predominant, accounting for 60% and 69% of the total MHFAs, respectively (p<0.05). These results demonstrate that the LA dcrivntives 9‐MODE and 13‐HODE. as well as the AA derivative 15‐1HETE, are esterified to PC, PI and PE of normal human epidermisin vito. The possibility remains that 9‐HODE. 13‐HODE anrl 15‐HETE, may incdiatc their biological cfrccts by