Lymphoma Pathology Panel and Repository (LPPR) review of pathologic material from 354 patients registered on Southwest Oncology Group clinical trials substantiated the diagnosis of Hodgkin's disease (Lukes-Butler classification) in 175 (94%) of 186 cases and the diagnosis of non-Hodgkin's lymphoma (Rappaport classification) in 162 (96%) of 168 cases. However, complete agreement (type and subtype) between institutional and LPPR review diagnoses was found in only 66% of confirmed cases of Hodgkin's disease and in only 58% of confirmed cases of non-Hodgkin's lymphomas. In 26 (16%) of 160 cases of non-Hodgkin's lymphoma, the initial interpretation of pattern (nodular vs diffuse) differed: 20 (25%) of 81 nodular lymphomas had been thought to be diffuse and 6 (8%) of 79 diffuse lymphomas had been diagnosed as nodular. The frequency with which initial diagnoses were confirmed on LPPR review was highest for three subtypes of lymphoma: nodular sclerosis Hodgkin's disease (88%), diffuse histiocytic lymphoma (86%), and nodular lymphocytic lymphoma (78%); rates of confirmation for all other subtypes ranged from 13-50%. The results of this analysis emphasize the necessity of having pathologic review of all cases entered on major lymphoma studies so that comparability of cases can be assured and the results of those studies placed in proper perspective.