The interleukin-2 (IL-2) receptor gamma-chain is a common component of several members of the cytokine receptor superfamily including those for IL-2, IL-4, IL-7, IL-9, IL-15, and possibly IL-13, and has recently been renamed the common gamma-chain (gamma c-chain). Transfection experiments have shown that the gamma c-chain participates in signal transduction by IL-2, IL-4 and IL-7, but a functional role for the gamma c-chain in biological responses by normal T cells and B cells to these cytokines has not been established. In this study, we have used X-linked severe combined immunodeficiency (X-SCID) as a naturally occurring gamma c-chain gene disruption model to examine the role of the gamma c-chain in human B-cell responses to IL-2, IL-4, IL-13, and IL-15. Our experiments show that B cells from two X-SCID patients with characterized gamma c-chain gene mutations do not respond to IL-2 or IL-15, but respond as well or better than normal B cells to both IL-4 and IL-13 in assays for B-cell activation, proliferation, and IgE secretion. This finding raises important questions about the function of the gamma c-chain in receptors for IL-4 and IL-13, and the nature of the immune defect in X-SCID.