The expression of the interleukin-2 (IL-2) receptor was studied in neoplastic cells derived from acute leukemias, T-cell lymphoblastic lymphomas, peripheral T-cell lymphomas, chronic lymphocytic leukemias, well-differentiated lymphocytic lymphomas, and established cell lines by both flow cytometric analysis and sodium dodecyl sulfate/ polyacrylamide gel electrophoresis (SDS-PAGE) after affinity crosslinking of radiolabeled IL-2. Cells from most acute leukemias (19 of 22), irrespective of their subtype (T, common or nonlymphoid leukemias), as well as T-cell lymphoblastic lymphomas and peripheral T-cell lymphomas expressed only the p70-75 β subunit of the IL-2 receptor. Cells from the more mature B-cell neoplasms, chronic lymphocytic leukemia, and well-differentiated lymphocytic lymphoma, expressed predominately αβ IL-2 receptors (11 of 14). In contrast to these results, most cell lines established from hematopoietic malignancies do not express either chain of the IL-2 receptor. Further studies are necessary to determine the exact function of the IL-2R p70-75 β subunit in immature hematopoietic cells, but its wide distribution throughout the hematopoietic system suggests that IL-2 may play a role in the early stages of hematopoiesis.© 1989 by Grune & Stratton, Inc. 0006-4971/89/7307-0038$3.00/0