Diethylstilbestrol (DES) at 0.019–0.025 mg/g body weight, fed with grain baits to Levante voles (Microtus guentheri [D. & A.]) of different age, sex and physiological condition, suppressed gestation for the first 10 days after mating. These doses, which are consumed voluntarily, also caused sterility in daughters of females which received DES at the end of pregnancy, and sterility or a significant delay (2–3 months) in sexual maturity of females which received it in their mother’s milk during the first days of life. DES had no significant effect on adult nonpregnant females or on males of any age, even if administered 3 days before mating.