Twenty-seven patients with advanced diffuse histiocytic lymphoma (reticulum-cell sarcoma) were treated with combination chemotherapy utilising nitrogen mustard (or cyclophosphamide), procarbazine, vincristine, and prednisone. Elven (41%) achieved a complete remission and only one of these has had a recurrence of tumour. The remaining ten complete responders were free of all evidence of tumour when last seen 26-105 months from the end of treatment. In contrast, all non-responders or partial responders have died. An interpretation of published survival data suggests that this virulent disease evolves quickly and is usally rapidly fatal if treatment is unsuccessful. Survival free of disease beyond 2 years from the end of treatment may be considered tantamount to cure. This definition of cure, previously applied only to patients treated with radiotherapy, seems applicable to patients who acheive complete remissions with modern drug treatment.