(+)-9α-Fluoro-11β-hydroxy-21-methoxy-16β-methyl-17α-propionyloxy-1,4-pregnadiene-3,20-dione (TS-410), a new synthetic adrenocorticosteroid, was administered s.c. at doses of 0.002, 0.004 or 0.008 mg/kg to New Zealand White rabbits (Std: NZW) during the period of fetal organogenesis (days 6 to 18 of gestation) to examine its effects on dams and their fetuses.In dams, no deaths were noted in any of the treated groups.However, the highest dose of 0.008 mg/kg induced abortion in a few animals and suppressed body weight gain.In fetuses, lethality, suppression of growth and teratogenic effects were noted in the 0.008 mg/kg group.Also, a weak teratogenic effect appeared to be present in the 0.004 mg/kg group.These findings suggested that the maximum no-effect dose of TS-410 was 0.004 mg/kg for dams and 0.002 mg/kg for fetuses.