This investigation is an examination of factors that affect eicosanoid (prostaglandin) concentrations in blood and their relationships to insulin and glucose concentrations. These parameters were evaluated in overweight college women participating in a Body Weight Management Program that emphasized weight reduction by moderate changes in dietary and lifestyle habits;A 12-hour fasting (fasted) and a 2-hour postprandial (fed) blood sample were obtained from 33 women at different stages of energy balance: (1) the initial phase of weight reduction when body weight loss was the most rapid (Sept. '82), (2) an intermediate stage when weight loss slowed down due to adaptation (Dec. '82), and (3) the final phase of the program when body weights for many of the participants had returned to or exceeded pre-reduction levels (Apr. '82). Eicosanoids (serum and plasma PGE(,1), PGE(,2)) concentration were measured by radioimmunoassay (RIA); plasma insulin by RIA; and, plasma glucose by the glucose oxidase method;Several significant correlations were found among the variables measured in this study. One of the most interesting was the positive correlation between Met-I(,2) concentrations and body weights. The greater amounts of adipose tissue and blood vessels (both of which produce Met-I(,2)) in an obese person compared to a normal weight individual justify this relationship;This study indicates that at least three factors may affect eicosanoid concentrations in blood. These include: (1) nutritional state (fasted or fed): the overall mean serum TXB(,2) concentration was significantly greater in the fed samples than in the fasted samples; (2) energy balance: a significant difference between fasted and fed serum TXB(,2) concentrations was found only in the Sept. samples when body weight loss was the most rapid. This trend suggests that the apparent effect of the nutritional state on serum TXB(,2) concentrations may be due in part to the energy balance of the females; and (3) season: generally, antiaggregatory eicosanoid concentrations (PGE(,1) and Met-I(,2)) were higher in Sept. than in Apr. Pro-aggregatory eicosanoid concentrations (PGE(,2) and TXB(,2)) were lower in Sept. than in Apr. In conclusion, at least three possible factors have been identified in this study that may influence eicosanoid concentrations in blood.