Abstract : The jet engine fuel designated JP-8 is the standardized fuel for the US military, which has resulted in exposure to both male and female personnel. Limited information is available on the reproductive effects of JP-8 jet fuel in humans and animals. In this report data are presented from two reproductive studies. In the first study male rats were given 0, 750, 1500 or 3000 mg/kg neat JP-8 daily by gavage for 70 days prior to mating with naive females to assess fertility and sperm parameters. After 70 days of dosing, body weights in the 3000 mg/kg group were over 30% lower than control weights. There were no significant changes for pregnancy rate, gestation length or sperm parameters as compared to control values. In the second study female rats were dosed with neat JP-8 (0, 325, 750, 1500 mg/kg) daily by gavage for a total of 21 weeks (90-day plus mating with naive males, gestation and lactation) in an effort to assess general toxicity, fertility and reproductive endponts. Results of the general toxicity segment revealed a significant dose-dependent decrease in body weights of the female rats. Significant organ weight ratio increases were seen for the liver: body, liver:brain and kidney:brain weights. Corresponding histopathologic changes and increase in liver enzymes (ALT, AST) were not observed although there was an increase in liver weight. Significant pathological changes were limited to squamous hyperplasia of the stomach and perianal dermatitis. In the reproductive and fertility segment, there were no statistically significant changes from control values for gestation length, pregnancy rate and number of pups per litter. There was a trend for decreased pup weight with increasing dose from postuat days 4 through 21 with the 1500 mg/kg pups statistically and biologically significantly lower on these days.