Several lines of research led to our hypothesis that perinatal exposure to TCDD may alter the sensitivity of adult rodents to the promotional effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on endometriosis. Pregnant rats and mice were treated on gestation day (GD) 8 with either 1 (rats) or 3 (mice) microg TCDD/kg or vehicle. Female offspring were reared to adulthood, and endometriosis was induced surgically. All animals received 0, 3, or 10 microg TCDD/kg 3 weeks prior to surgery, at the time of surgery, and 3, 6, and 9 weeks after surgery. Necropsies were performed 12 weeks after surgery. Measurements at necropsy included the diameter of endometriotic lesions and body, uterine, ovarian and liver weights. While no effect of treatment on lesion diameter was found in rats, analyses revealed that perinatal plus adult exposure to TCDD can increase the size of endometriotic lesions surgically induced in mice. These and additional data on body and organ weights are consistent with previous work. These data confirm the sensitivity of mice to the promotion of endometriotic lesion growth by TCDD and indicate a perinatal effect of TCDD on this parameter when perinatal exposure on GD8 is supplemented with adult exposure to TCDD of female mice.