In the medical management of ectopic pregnancy, human chorionic somatomammotropin (hCS) proved to be a more sensitive indicator of continued trophoblastic activity than either beta-human chorionic gonadotropin (beta-hCG) or progesterone (P). In the authors' series of 21 women treated with methotrexate for ectopic pregnancies, only two ruptured. In both cases, hCS levels continued to rise during and after methotrexate treatment. Concomitantly, beta-hCG and P decreased in both of these patients. The authors thus interpret increasing hCS as a reflection of continued syncytiotrophoblast growth, signalling impending rupture. Furthermore, patients with levels of hCS less than 10 ng/ml may require neither medical nor surgical therapy.