Reproductive parameters in Fischer 344 rats were evaluated following inhalation of propylene oxide (PO) for two successive generations. Thirty male and 30 female rats were exposed to 0, 30, 100, or 300 ppm PO for 6 hr/day, 5 days/week for 14 weeks and then mated to produce the f1 litters. After weaning, 30 randomly selected f1 pups/sex/group were exposed to PO for 17 weeks and subsequently mated to produce the f2 litters. Reproductive parameters examined included fertility, litter size and neonatal growth, and survival. All adults and selected weanlings were examined for gross and histologic lesions. Toxicity due to PO was demonstrated by decreased body weights of parental f0 and f1 rats at 300 ppm. No treatment-related effects on fertility (mating or conception) were observed in either f0 or f1 matings. Neonatal survival indices for f1 or f2 litters revealed no treatment-related effects. Litter size was decreased in the f1 rats exposed to 100 ppm PO. However, the litter size in the 300 ppm group was comparable to the control group, and no effect on litter size was shown in PO-exposed f2 litters. Pup weights were unaffected by parental exposure to PO in either generation. Pathologic examination of adults and weanlings revealed no changes considered due to PO. Based on these results, it is concluded that inhalation exposure to PO at levels up to 300 ppm over two generations did not produce any adverse effects on reproductive function.