Successful treatment of four, non ruptured, cases of interstitial pregnancy are reported. Treatment consisted of in situ injection of methotrexate during coelioscopy. Dosage was 1.5 mg methotrexate per kilogram body weight. Negative plasma beta hCG levels were obtained 9 to 22 days after conservative medical treatment. No clinical or biochemical side effects were observed. Of two patients had no radiologically demonstrable cornual abnormality on the hysterosalpingographies effected at the 3 months evaluation after ascertained interstitial pregnancy, one have normal pregnancy. Two further patients had normal uneventful pregnancies 12 to 15 months later. Treatment of interstitial pregnancy by way of one in situ injection of methotrexate seems to be the currently preferred alternative to classical surgery.