Adult female rats having regular ovarian cycles were treated with 2.5, 5 or 10 mg/kg cadmium chloride (CdCl2) during estrus or diestrus and mated 32, 80 or 132 h post-treatment. Sperm positivity was checked next day on the predicted estrus. Maternal effects during pregnancy, fetal outcome on day 10 or at term as well as postnatal development of the F1 generation were recorded. CdCl2 caused sterility in 40 or 87% of animals at doses 5 and 10 mg/kg, respectively. Influence of Cd on fertility depended on the day of the cycle, and on the time elapsed between treatment and mating. The Cd-caused overt toxicity in fertile female rats was expressed by dose-dependent decrease in maternal body weight gain and increased progesterone blood levels. No treatment-related alteration in number and weight of conception day 10 of pregnancy or in weight and size of litters, rate of males and females at term and during the 21-day post-parturition study could be seen. It is concluded that Cd given prior mating may lead to sterility in a dose-dependent fashion. This is suggested to be caused by anovulation resulting from reversible pituitary disfunction. Animals proving fertile in spite of Cd-treatment have developed tolerance against Cd in terms of fetal outcome and postnatal development.