Immunoperoxidase markers are useful and often essential in distinguishing among lymphocyte-predominant Hodgkin's lymphoma, T-cell-rich B-cell lymphoma, and lymphocyte-rich classic Hodgkin's lymphoma. However, it is becoming increasingly clear that these "entities" are closely related clonal B-lineage neoplasms that may intertransform and/or coexist. We hypothesized that, just as there are cases with morphologic overlap, there would also be immunophenotypic overlap that would be found when a series of such cases is studied in detail. Eight cases of lymphocyte predominant Hodgkin's lymphoma, eight cases of lymphocyte-rich classic Hodgkin's lymphoma, seven cases of T-cell-rich B-cell lymphoma, and four cases of large B-cell lymphoma with focal features of T-cell-rich B-cell lymphoma were examined by the immunoperoxidase technique for expression of CD3, CD15, CD30, CD20, CD57, epithelial membrane antigen, and Epstein-Barr virus latent membrane protein (EBV LMP). All eight of the lymphocyte-predominant Hodgkin's lymphoma cases had CD20+ lymphocytic and histiocytic cells and CD57+ rosettes; however, in two cases, occasional lymphocytic and histiocytic cells were also weakly positive for CD15, CD30, and EBV LMP. Among the eight lymphocyte-rich classic Hodgkin's lymphoma cases, CD15+ Reed-Sternberg (R-S) cells were found in seven; however, in three of these cases rare rosettes of CD57+ cells surrounded the R-S or lacunar cells. In one case of large B-cell lymphoma the malignant cells resembled R-S cells and were CD20+, EBV LMP+, CD30+, CD15-, and surrounded by rosettes of CD57+ T cells. The majority of the cases exhibited the "expected" immunophenotypic patterns; however, the exceptional cases that were found serve to confirm the interrelationship among these clonal B-lineage neoplasms.