Thirty-six patients presenting with stage II-IV primary gastrointestinal non-Hodgkin's lymphoma of high-grade pathology were treated in a prospective study from 1975 to 1983 with combined modality therapy. A complete response rate of 56% was obtained and the overall 5-yr survival rate was 36%. The 5-yr relapse-free survival rate of the complete remitters was 79%. Multivariate analysis revealed that the remission achieved (P less than 0.001) and the completeness of primary surgery (P = 0.018) would reliably predict the duration of overall survival. The finding of diffuse histiocytic histology (Rappaport) predicted longer relapse-free survival. The majority of deaths were related to intra-abdominal complications and not to disseminated lymphoma. Gastrointestinal tract non-Hodgkin's lymphoma of high-grade pathology of all stages is curable with a combination of chemotherapy and radiotherapy following surgery to remove as much macroscopic disease as is possible.