We investigated a simple method using induced ovulation in immature rats to detect ovarian injury due to chemicals. We investigated the influence of di-(2-ethylhexyl) phthalate (DEHP) on ovulation induced by equine chorionic gonadotropin (eCG) in immature F344 rats. Single injections of 15 and 30 iu eCG induced ovulation in 4 of 6 rats and in all of 4 rats, respectively. The mean number of ovulated ova was 12.7 in the 15 iu eCG group and 8.0 in the 30 iu group. When rats received 4 daily doses of DEHP at 500 mg/kg, ovulation occurred in 4 of 6 rats in the 15 iu eCG group and in 1 of 3 rats in the 30 iu group. Mean numbers of ovulated ova were 2.50 and 0.33 ova in the 15 and 30 iu groups, respectively. Changes in ovarian and uterine weights were not found. Inhibition of ovulation by the injection of DEHP indicated the utility of induced ovulation in immature rats to detect reproductive toxicity in females.