The capability to form rosettes with sheep erythrocytes (E), antibody-complement-sensitized ox erythrocytes (EAC) and autologous erythrocytes (ARFC), and surface immunoglobulin determinations were studied using 21 lymph nodes and one tonsil with pathologically-proven non-Hodgkin's lymphoma and 10 lymph nodes with benign pathology. Fourteen of 22 non-Hodgkin's lymphoma patients (64%) had a high incidence of E-rosette formation and they were further differentiated into ARFC-positive and ARFC-negative lymphomas. The clinicopathological findings of the latter were compatible with those of adult T-cell leukemia. ARFC-positive lymphoma was regarded as non-Hodgkin's lymphoma of T-cell type and one patient showed lymphoblastic lymphoma with high ARFC counts. ARFC counts were very low in B-cell and non-T, non-B lymphomas. The results from benign lymph nodes were too variable to draw any conclusion, although ARFC counts were relatively high in lymphadenitis and hyperplasia.