78 patients with malignant epithelial ovarian tumours were treated with a new cytostatic, didydroxybusulfan (Treosulfan), which belongs to the group of alkylating agents. The treatment was given intermittently, mostly in the outpatient department. The period of observation was from three years to six months. II patients did not complete one course of treatment for several reasons. Two stage Iapatients received prophylactic treatment following a radical operation. No follow‐up for one patient. The main group consists of 64 patients, 29 with recurrences and 35 with tumour residues following a non‐radical operation. Of the latter we have 6 in stage IIb, 22 in stage III and 7 in stage IV. 45% of the main group showed excellent and good response, 55% poor or no response. The mean survival time for cass with excellent and good response was twice as long as that recorded for cases with poor or no response (12 and 6 months). In the group responding most favourably, the tumours were mainly comparatively poorly differentiated. Ascites disappeared entirely for more than 3 months in 19 out of 29 patients. Two patients previously inoperable could be radically operated after treatment. The only toxic effect was bone marrow depress