Sarin (Agent GB, isopropyl methylphosphonofluoridate) is an organophosphate cholinesterase inhibitor. Sarin (Type I or Type II) was administered by gavage to CD rats on d 6-15 of gestation at dose levels of 0, 100, 240, or 380 micrograms/kg/d and to New Zealand White (NZW) rabbits on d 6-19 of gestation at dose levels of 0, 5, 10, or 15 micrograms/kg/d. Females were weighed on gestational days (GD) 0, 6-16 for rats and 6-20 for rabbits, and immediately prior to termination (GD 20 for rats and GD 29 for rabbits). All animals were monitored daily for clinical signs of toxicity throughout dosing and until sacrifice. At necropsy, gravid uteri were weighed and examined for the number and status of implants (live, resorbed, or dead). Individual fetal body weight, malformations, and variations (external, visceral, and skeletal) were recorded. Rat and rabbit dams in the high-dose groups exhibited significant signs of maternal toxicity and increased maternal mortality. Examination of gravid uteri revealed no statistical differences among treatment groups in the incidence of resorptions or of dead or malformed fetuses, or in average body weight of live fetuses per litter. These results show no evidence or developmental toxicity in the CD rat or NZW rabbit following exposure to either Type I or Type II sarin during embryonic differentiation and major organogenesis, even at a dose that produced maternal toxicity.