SUMMARYA facile retro-synthesis involving the radical chain decarboxylation of the Nhydroxypyridine-2-thione esters of both arachidonic and docosahexaenoic acid was utilized to synthesize (all Z)-l-bromononadeca-4,7,10,13-tetraene, and (all Z)-l-bromoheneicosa-3,6,9,12,I5,18-hexaene in 60% overall yield. The corresponding polyhomoallylic magnesium bromides were carbonated with [I1C]CO2 to afford the I-[llC]polyhomoallylic labeled fatty acids in good yield in less than 35 minutes. The final radiochemical purities were found to be in excess of 95% by radio-HPLC.