Tetrahydrofuran (CAS No. 109-99-9) was evaluated for developmental toxicity. In part I of the experiment the test material was administered to 14, 7, 7, 7, and 7 CD rats by inhalation at exposure levels of 0, 200, 500, 2500, and 5000 ppm, respectively on gestational days 6-15. In part II, 29, 87, and 38 CD rats were administered the test material by inhalation at exposure levels of 0, 1000, and 5000 ppm, respectively from days 6-15 of gestation. In both parts I and II, no maternal deaths occurred but the 5000 ppm exposure induced significant decreases in feed consumption (p<0.05) and body weight gain (p<0.05) along with absence of response to noise stimulus during the exposure period, followed by lethargy and incoordination for 1 hour post-exposure. No toxic responses were observed at 200 or 500 ppm (part I). At 1000 ppm (part II) and 2500 ppm (part I) only a reduced response to a noise stimulus was observed in comparison to controls. The mean number of implantations per dam and the incidence of malformed fetuses were not exposure related (among part I or part II). At 5000 ppm, the fetal variations of reduced weight and less ossified sternae were significantly different (p<0.05) from controls (for both part I and part II). Embryotoxicity expressed as developmental delay occurred at 5000 ppm.