A two-generation reproductive toxicity study was conducted with groups (F0 and F1) of 30 female and male Fischer 344 rats exposed by inhalation to propylene oxide at analytically determined (method not reported) concentrations of 0, 0.07, 0.24 or 0.71 mg/l for 6 h/d. These exposure levels were chosen based on a chronic study which resulted in a loss of body weight at the highest concentration (0.71 mg/l). F0 and F1 rats were exposed 5 d/week during the pre-mating period (from 7 weeks of age for 14 weeks until mating for the F0 animals and from 4 weeks of age for 17 weeks until mating for the F1 animals) and 7 d/week during mating, gestation and lactation. Maternal animals were not exposed from gestation day 21 through the fourth day postpartum. Observations of the F0 and F1 animals included treatment-related decreased body weights in low-, mid- and high-dose males and high-dose females. There were no treatment-related reproductive effects. Gross necropsy of F0 and F1 adults and F1 and F2 weanlings and histopathological exam of control animals and high-dose F1 and F2 weanlings revealed no treatment-related changes.