It has been suggested that tamoxifen may improve the efficacy of medical castration with luteinising hormone-releasing hormone analogues, but very few data have so far been published concerning the clinical and endocrinological activity of this therapeutic modality. In this phase II multicentre trial conducted by the Italian Trials in Medical Oncology group (ITMO), 64 premenopausal patients with hormone receptor-positive or unknown breast cancer were treated with monthly s.c. injections of goserelin 3.6 mg, in association with a tamoxifen daily dose of 20 mg, as first-line therapy for their advanced disease. All of the patients were evaluable for efficacy and there was an overall response rate of 41% (95% confidence interval 28-52%), with 7 of the 26 responders achieving complete remission. The median time to response was 4 months (range 2-17), and the median response duration was 13 months (range 6-37 +). Better responses were observed in soft tissues (51%); the response in visceral and bone metastases was respectively 19% and 37%. Serum concentrations of gonadotrophins and oestradiol were significantly decreased by the treatment, oestrogen levels being constantly suppressed to within the range observed in post-menopausal women. No significant change was detected in serum testosterone levels. In our experience, although it was not associated with any increased clinical efficacy, the concurrent use of goserelin and tamoxifen proved to be a feasible approach in the management of premenopausal advanced breast cancer.