In this pilot clinical trial conducted in 10 postmenopausal women with advanced breast cancer, we evaluated the endocrine effects and toxicity of combined somatostatin analog and dopaminergic therapy in the attempt to suppress both growth hormone (GH) and prolactin (PRL) secretion. The patients' mean age was 63 years (range: 54-77) and the average number of previous treatments was 4.8 +/- 2 (SD). All patients were treated with the somatostatin analog SMS 201-995 (100-200 micrograms s.c. in a.m. and h.s.) and bromocriptine (2.5 mg orally twice a day). During treatment, GH levels following provocative testing (either L-DOPA or insulin-induced hypoglycemia) were suppressed in 7/9 patients. Basal somatomedin-S (Sm-C) levels declined in 6/9 women. Both GH and Sm-C levels decreased in 4 patients, while in the remaining 5 only one of the two parameters was lowered on treatment. PRL secretion (during provocative TRH testing) was almost totally abolished in 8/9 patients. The treatment did not affect circulating levels of FSH, LH, E1, E2, E1-S, T4, T3RU, or cortisol. Seven patients experienced no side effects. Nausea occurred in 3, but was severe enough in only one to require discontinuation of therapy. One patient experienced disease stabilization consisting of less than 50% regression of skin nodules and pleural effusion, a decline in CEA titer, and an improved performance status lasting 7 months. We conclude that combined SMS 201-995 and bromocriptine therapy is safe and frequently suppresses GH and PRL secretion. Its role in the treatment of metastatic breast cancer should be tested in patients with less advanced disease.