The neoplastic lymphoid cells in 33 patients with chronic lymphocytic leukemia (CLL), 1 case of prolymphocytic leukemia (PLL), and 29 patients with various types of non-Hodgkin's lymphoma (NHL) were examined for the expression of transferrin receptors (TR) using a panel of three anti-TR monoclonal antibodies (MAb). Both immunofluorescence and immunoperoxidase techniques were applied in each case. All cases of B-CLL (31) were negative for TR expression, while both the cases of T-CLL, and the only case of T-PLL showed significant TR-positive cell populations. Similarly, all 13 cases of "low-grade" NHL were TR negative, while 6 of 7 cases of "high-grade" lymphomas (lymphoblastic and immunoblastic) had up to 28% TR-positive cells. A proportion (4/9) of "intermediate grade" lymphomas had 10-15% TR positivity. Interestingly, the majority of B-leukemia/lymphoma (49/55) cases were TR negative, while all 8 cases of T-cell leukemia/lymphoma were TR positive. This clearcut association of TR expression with high-risk morphologic and immunophenotypic subgroups of lymphoid leukemia/lymphoma points to the potential role of TR as a prognostic marker in lymphoproliferative disorders.