Somatostatin analogues have been shown to suppress some hormones and growth factors involved in breast tumour growth and a direct in vivo and clinical antimumour effect has recently been reported. In our study the effects of tamoxifen, combined with a depot somatostatin analogue in 33 postmenopausal untreated breast cancer patients, have been evaluated. Blood samples were obtained before treatment, after 14 days and then monthly, in order to evaluate the behaviour of serum IGF-I, GH and somatuline levels. The drug combination resulted in a significant and synergistic reduction of plasma IGF-I concentration. No significant changes of serum GH were observed. 12.5% of patients exhibited a complete response and 37.5% a partial response for an overall objective response rate of 50% (95% CL 35-69%). The high remission rate reported, the absence of overlapping side effects between tamoxifen and somatuline and the synergistic activity on IGF-I suppression justify a further evaluation of the drug-combination.