Chemotherapy of neuroendocrine tumors must be improved. The most widely used regimen, which combines streptozotocin with fluorouracil, commonly obtains poor results. The best response rate that has been reported for carcinoid tumors is 33%. From July 1991 through September 1994, 18 patients who had advanced neuroendocrine tumors-including nine carcinoid tumors, seven neuroendocrine tumors of unknown primary site, one insulinoma, and one paraganglioma-were treated with a regimen of dacarbazine, 400 mg/m2/day, plus fluorouracil, 1 g/m2/day, with leucovorin, 200 mg/m2/day, for 2 days every 21 days (DTIC-LVFU2 protocol). The results were assessed according to the World Health Organization criteria of toxicity and response. Toxicity was moderate. The most severe side effects were grade 3 vomiting in two patients, grade 3 leukopenia in three patients, and grade 3 mucositis in one patient. The overall response rate was 27%, with only one partial response for carcinoid tumors but one complete and three partial responses for the other tumor types. Efficacy was insufficient in patients who had carcinoid tumors but the combination of dacarbazine with fluorouracil and leucovorin could be an effective regimen for the treatment of neuroendocrine tumors of unknown primary site.