To determine the possible activity of cyclooxygenase and lipoxygenase like enzymes in Drosophila melanogaster, we have investigated whether fly homogenates can biosynthesize prostaglandins and HETEs. Incubation of fly extracts with AA yields a mixture of 15- 12- 9- and 8-HETE as detected by selected ion monitoring GC-MS. Also the combination of HPLC-RIA using a PGE antibody shows the presence of endogenous PGE2 immunoreactivity in the extracts (405 pg/g in males and 165 pg/g in females). We have also detected the presence of lipoxygenase like immunoreactivity in the reproductive male system by using immunocytochemical techniques in whole body sections of the fly as well as reactivity in the digestive system of both males and females. Finally, we have not been able to detect endogenous AA in the fly by GC-MS methods. However, estimates by GC-MS of the total body fatty acids indicate substantial amounts of potential AA precursors.