Between June 1981 and May 1988, 51 children with diffuse undifferentiated, advanced (Murphy Stage III and IV) intra-abdominal non-Hodgkin's lymphoma were treated on an intensive multi-drug chemotherapy protocol without irradiation to the primary tumour. Therapy was completed for Stage III disease at one year, but Stage IV patients continued with a further year of therapy until January 1986, when it was reduced to one year. Central nervous system (CNS) prophylaxis consisted of eight doses of intrathecal MTX for all children, and 24 Gy cranial irradiation for Stage IV patients only. There were 42 patients with Stage III disease (III A n = 29 and III B n = 13) and nine patients with Stage IV disease, of whom eight had extensive bone marrow and extramedullary disease (FAB L3 ALL). No patient had CNS disease at presentation. Forty-eight of 51 children (94%) achieved a complete remission. Two children died during remission induction therapy and eleven children relapsed, mostly within eight months of diagnosis. All patients have completed therapy. Failure free survival is 76% for Stage III and 67% for Stage IV patients, with a median followup of 90 and 64 months, respectively. Subdividing Stage III patients into Stage III A and III B did not show significantly different survival (P = 0.9), but the number of patients in Stage III B is small. These results compare favourably with the most effective published protocols, and toxicity has been manageable.