Preliminary data would suggest that the pineal hormone, melatonin (MLT), may enhance tamoxifen (TMX) anti-tumour efficacy. Both MLT and TMX have been used as single agents in the palliative treatment of metastatic neoplasms, other than the classical hormone-dependent tumours, without, however, any clear efficacy. On this basis, a phase II study with TMX plus MLT has been performed in untreatable metastatic solid tumour patients. The study included 25 metastatic solid tumour patients other than breast cancer and prostate cancer (six unknown primary tumour; four melanoma; four uterine cervix carcinoma; five pancreatic cancer; three hepatocarcinoma; two ovarian cancer; one non-small-cell lung cancer), for whom no other effective standard therapy was available, because of poor clinical conditions, no response to previous chemotherapies and/or chemotherapy-resistant tumours. Both drugs were given orally every day until disease progression (TMX, 20 mg day-1 at noon; MLT, 20 mg day-1 in the evening). Three patients had a partial response (PR) (12%; 95% confidence limits 2-24%) (one cervix carcinoma; one melanoma; one unknown primary tumour). A stable disease (SD) was achieved in 13 other patients, whereas the remaining nine patients progressed. Performance status (PS) improved in 9/25 patients, whose median score increased from 50% to 70%. Finally, a survival longer than 1 year was observed in 7/25 (28%) patients. This phase II study would suggest that the neuroendocrine combination with TMX plus MLT may have some benefit in untreatable metastatic solid tumour patients, either in controlling cancer cell proliferation or improving the PS.