AbstractPretreatment of pregnant BALB/c mice with several low doses of tolbutamidc protected against the fetolethal effects of a high dose. Pregnant mice were given single ip injections of 400 mg/kg in saline on day 13; 100 mg/kg/day on clays 10, 11, 12, and 13; or 100 mg/kg/day on days 10, 11, and 12 and 400 mg/kg on day 13. On day 16 the single‐treatment group had a significantly higher resorption rate than any other group. Fetolethality was not related to hypoglycemia. The protective effect of pretreatment may have been due to induction of maternal microsomal enzyme