The reproductive toxicity of a single oral dose/mouse (15-50 mg/kg) of cyclopiazonic acid (CPA) in the early phase of pregnancy (day 2-8) was investigated. Male mice used in this study were untreated. A limited number of pregnant mice were treated with 66 mg/kg ergonovine maleate (po, sc) to compare its effect with that of an equivalent dose of CPA (50 mg/kg). Among control sperm-positive mice treated with po NaHCO3 solution, 97.5% were gravid on necropsy day (pregnancy day 12). A single dose of CPA (15-50 mg/kg, po) given on days 2 to 8, decreased the pregnancy rates significantly. In groups treated with a single dose of CPA on pregnancy day 4 to 8, vaginal hemorrhage was observed 1 to 7 days after treatment, and it usually resulted in termination of pregnancy (abortion). Fetal resorption rates were higher than the control rate only in the groups treated with 30 mg/kg CPA po on day 4 or 8. CPA decreased body weight gains and the weights of uteri with fetuses. The ovary weights were generally not changed. Ergonovine maleate (66 mg/kg, sc, po) had no significant effect on all of the parameters examined. The estrous cycle returned without any delay in sperm-positive mice in which nidation of fertilized eggs had been inhibited by CPA, and also in nonpregnant mice (used for the LD50 determination) surviving near lethal doses of CPA (50-70 mg/kg, po). The oral LD50 value for CPA in nonpregnant mice was 64 +/- 4.4 mg/kg, and the toxicity signs were ptosis, hypokinesia, hypothermia, action tremor, cessation of food and water intake and resulting cachexia. The duration and intensity of these toxic signs were dose dependent.