A single institution prospective trial was conducted to evaluate the efficacy of biotherapy or chemotherapy in metastatic neuroendocrine carcinomas (NECs). The choice of therapy was based on the revised histological classification criteria of the WHO in an effort to define a standardized protocol for therapy of these cancers. Patients with well-differentiated NECs (WD-NECs; n=11) received therapy with octreotide long-acting release and interferon-α-2b for a maximum of 1 year; cases with poorly-differentiated NECs (PD-NECs; n=8) were given combination cisplatin, L-leucovorin and 5-fluorouracil chemotherapy for a maximum of 9 cycles. Five patients (4 with WD-NECs) had carcinoid syndrome. Among the patients with WD-NECs (median follow-up 20 months, range 4-40), 4 had partial responses and 7 had stable disease. In patients with PD-NECs (median follow-up 10.5 months, range 3-30), 3 had partial response, 2 stable disease, and the disease progressed in 3 cases. The 2-year survival rate in WD-NECs and PD-NECs was 88% and 66%, respectively. Grade 3-4 side-effects were limited to 9% thrombocytopenia and 12.5% neutropenia. Both these treatment regimens had a good therapeutic index and compared favourably with those previously reported for metastatic WD-NECs and PD-NECs.