Prolactin (PRL) constitutes a growth factor for breast cancer cell proliferation and abnormally elevated blood concentrations of PRL are associated with poor prognosis and reduced efficacy of antitumor therapies in metastatic breast carcinoma. It has already been demonstrated that low-dose bromocriptine, an antiprolactinemic long-acting dopaminergic drug, normalizes PRL blood concentrations in metastatic breast cancer patients with abnormally elevated PRL levels. In addition, previous clinical studies have already demonstrated a lower efficacy of chemotherapy with taxotere in metastatic breast cancer, with persistent hyperprolactinemia. We planned a controlled clinical study to evaluate the influence of a concomitant administration of the antiprolactinemic drug bromocriptine on the efficacy of chemotherapy with taxotere, in metastatic breast cancer patients progressing after chemotherapeutic combinations containing anthracyclines. The study included 30 randomized consecutive patients treated with taxotere alone or taxotere plus bromocriptine. Taxotere was given I.V. at 100 mg/m2 every 21 days for 3 cycles. Bromocriptine was given orally at 2.5 mg/day every day until the end of the chemotherapeutic treatment. Bromocriptine therapy induced a significant decline in PRL mean blood concentrations compared to patients treated by chemotherapy alone. No complete response was obtained. A partial response (PR) occurred in 5 out of 14 (36%) patients treated with taxotere plus bromocriptine and in only 2 out of 16 (13%) patients treated with taxotere alone. Moreover, a stable disease (SD) was obtained in 5 out of 16 patients treated with taxotere alone and in 7 out of 14 patients concomitantly treated with bromocriptine. Therefore, the percent of non-progressive disease (PR + SD) achieved in patients treated with taxotere plus bromocriptine was significantly higher with respect to that found in patients treated with taxotere alone (12 out of 14 vs 7 out of 16, p < 0.025). This preliminary clinical study would suggest that the inhibition of PRL secretion by antiprolactinemic drugs such as bromocriptine may enhance the efficacy of chemotherapy for metastatic breast cancer.