Lymph nodes were obtained from 28 patients with non-Hodgkin's lymphoma and 24 patients without hematologic malignancy. Cases of undifferentiated lymphoma, diffuse histiocytic lymphoma, diffuse and nodular mixed histiocytic-lymphocytic lymphoma, nodular poorly differentiated lymphocytic lymphoma, and diffuse well differentiated lymphocytic lymphoma were analyzed. Touch preparations were stained for nonspecific esterases, peroxidase, Sudan black B activity and with periodic acid-Schiff and Wright-Giemsa reagents. Mononuclear cell suspension from lymph nodes and, in some cases, peripheral blood were tested for spontaneous rosette formation with sheep erythrocytes and for the presence of surface immunoglobulin. The remainder of the lymph node was examined after staining with hematoxylin and eosin. Analysis of the lymphocyte surface markers indicated that 15 cases of various histologic types of lymphoma were B cell proliferations. However, three out of four cases of diffuse poorly differentiated lymphocytic lymphoma and one of seven cases of diffuse histiocytic lymphoma appeared to represent T cell neoplasia. Lymph nodes from four cases of lymphoma representing diverse histologic types were replaced by neoplastic cells devoid of discernible cell markers. In five cases, the distribution of cell surface markers in the malignant lymph node failed to differ from data obtained in the analysis of non-neoplastic lymph nodes. The study indicates that the histopathologic entities recognized in the currently employed classification of lymphoreticular malignancies are heterogeneous. Alterations in the distribution of cell surface markers in the peripheral blood from five of 12 patients indicated involvement prior to demonstrable morphologic evidence of peripheral blood involvement in four patients and bone marrow infiltration in two patients.