To investigate the possible relationships between immunologic phenotype, histologic subtype, and clinical features in diffuse, large cell lymphoma (DLCL), a computerized registry has been established for the prospective collection of immunologic, histologic, and clinical data. A combination of immunofluorescence and immunoperoxidase technics on single-cell suspensions, frozen tissues, and B5-fixed, paraffin-embedded specimens was used to study the first 33 biopsies. A definitive phenotype was established in all but two cases. Monoclonal antibody reagents reactive in B5-fixed, paraffin-embedded tissue sections helped assign a B-cell lineage in four cases lacking surface or cytoplasmic immunoglobulin, monoclonal light chains, and T-cell markers. There was no statistically significant association between the immunologic phenotype (whether mature B or not) and any clinical or histologic parameter, including response to therapy and survival. Bone marrow involvement was found to be associated significantly with both vague nodularity and a cleaved cell subtype. Through the use of a multifaceted approach to the immunophenotypic analysis of the DLCLs, a distinct lineage and stage of differentiation could be assigned to most biopsy specimens. That such analysis has significant clinical implications for patients with DLCL could not be demonstrated in this series.