In order to investigate the pineal function and its relation with the hypophysis in human neoplasms, melatonin and GH serum levels were determined in 63 patients, 42 affected by solid tumours and 21 by lymphoma or leukaemia. In women with breast cancer PRL was also measured. Melatonin, GH and PRL were evaluated in 52 healthy subjects acting as controls. The oncological patients showed significantly higher mean melatonin serum levels than the control subjects. Mean melatonin values were lower in patients with solid tumours who had metastases, than in cases without metastases. Chemotherapy caused an evident decrease in melatonin levels. Surgery was followed by a fall in melatonin in patients without metastases. Mean GH serum levels observed in oncological patients were similar to those in control subjects and were not influenced by therapy. PRL levels were within the normal range in women suffering from breast cancer.