The effect of streptozotocin (STZ)-induced diabetes in neonatal male rats on plasma lipids and aortic 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) synthesis in adult life was investigated. A reduction (62% of control) in aortic 6-keto-PGF1 alpha was observed only after maturity, at 17, but not 8, weeks of age. In contrast to STZ-induced diabetes in adult rats, who experience marked elevations in both plasma triglyceride (TG) levels (up to 13-fold) and total cholesterol (CH) levels (2-fold), plasma TG levels were never elevated and plasma total CH levels were significantly elevated (37%) only at 17 weeks of age. Thus, the reduction in aortic 6-keto-PGF1 alpha synthesis was dissociated from alterations in plasma TG levels in adult male rats with diabetes of neonatal origin. A significant elevation (0.31 to 0.48) in the proportion of linoleate (a competitive inhibitor of prostacyclin synthesis) to arachidonate in aortic phospholipids was also found. The results suggest that the reduced aortic synthesis of 6-keto-PGF1 alpha occurring in diabetic rats was not related to hypertriglyceridemia, but may have been related to hypercholesterolemia or altered ratios of linoleate to arachidonate in aortic phospholipids.