Sixty-seven evaluable patients with mixed cellular and histiocytic lymphomas, both nodular and diffuse, were treated with a combined drug regimen of BCNU, cyclophosphamide, vincristine, and prednisone administered for six monthly courses. Of 28 previously untreated patients with diffuse histiocytic lymphoma, 14 (50%) achieved a complete remission, and an additional 7 (25%) had a good partial response for an overall remission rate of 75%. Complete remissions were also obtained among the small number of mixed and nodular histiocytic lymphomas which were treated. The median survival for previously untreated patients with diffuse histiocytic lymphoma who achieved a complete remission is nearly two years and 42% (8/19) of these patients remain in their initial unmaintained remission (range 2-119 weeks). Hematologic toxicity, although acceptable, was the limiting factor. Granulocytes were more often and more severely depressed than platelets.