Twenty-five lymph nodes from patients with non-Hodgkin's lymohomas were evaluated by immunologic technics applied to cell suspensions and tissue sections. Malignant lymphomas with cytologic characteristics similar to those of neoplastic cells were found to be immunologically heterogeneous. The distribution as well as the number of neoplastic cells with distinctive immunologic surface markers could not be related to the cytologic type of malignant lymphomas. The number of malignant cells simultaneously expressing the T- and B-cell markers was increased in malignant lymphoma nodes. Cells positive for the triple markers (Ig+, EAC+, T+, where Ig = immunoglobulin, EAC = erythrocytes sensitized with antibody and complement, and T = T marker) represented the predominant population in these nodes, and the distributions of these cells were useful in diagnosis. Monoclonal immunoglobulins were detected in all lymphoma cells but not in the patients' sera. The tissue distribution of EAC-positive cells may have a prognostic significance. The paucity of cells with the Fc receptors was a characteristic feature of all lymphoma cells studied. Evaluations of immunologic markers on lymphoma cells in conjunction with the histologic characteristics may provide a sounder basis for diagnosis.