The expression of interferon-y (IFN-y) receptors on normal human B cells and four B cell lines was studied. Recombinant human IFN-y was labeled with [y-32P]ATP using the catalytic subunit of a cAMPdependent protein kinase. All four B cell lines, although differing in their responsiveness to IFN-7, were found to express highaffinity receptors (1,000-1 1, OOO receptors/cell). Normal unactivated B lymphocytes were also found to express constitutively high-affinity receptors, approximately 1,400 receptors per cell with an estimated affinity of 295 pM. Activation of the normal B cells in vitro with the polyclonal B cell activator, Staphylococcus aureus Cowan strain I (SAC), resulted in a slight decline in receptor number and a more pronounced fall in receptor density. One of the B cell lines and unactivated normal B cells were shown to internalize labeled IFN-y rapidly. Chemical cross-linking of "P-IF"-y to the CB B cell line and to freshly isolated B lymphocytes revealed one major cross-linked receptor-ligand complex which had an estimated molecular weight of approximately 110 kilodaltons. This complex corresponded to a 93 kD receptor cross-linked to recombinant IFN-y. Our data indicate that normal B lymphocytes constitutively express an approximately 93 kD IFN-y receptor which is similar to the receptor present on Epstein-Barr virus-transformed B cell lines.