Fatty acids and their derivatives are involved in events associated with reproduction in invertebrates. The purpose of this study was to investigate the presence and variation in amount of selected fatty acids during vitellogenesis in the crayfishProcambarus paeninsulanus.Particular attention was given to possible precursors of eicosanoid production. Ovarian homogenates were prepared and analyzed by gas chromatography. Results demonstrated a dramatic increase in several fatty acids fiom the onset of secondary vitellogenesis to just prior to ovulation. It is possible that unsaturated fatty acids or their derivatives may be involved in the importation of exogenous proteins to support yolk formation. In addition, results demonstrate ample substrate exists in crustacean ovaries to support production of reported eicosanoids by lipoxygenase andfor cyclooxygenase pathways.