We isolated a cDNA clone for the gamma chain of the mouse interleukin 2 receptor. Introduction of the mouse gamma chain cDNA clone into a mouse fibroblast cell line, L929, expressing the mouse alpha beta heterodimer IL-2 receptor converted pseudo-high affinity of the IL-2 receptor into functional high, resulting in internalization of IL-2 and induction of the c-myc, c-fos and c-jun genes. The mouse beta gamma heterodimer, however, failed to bind IL-2 unlike the human beta gamma heterodimer intermediate-affinity receptor. These results indicate that the mouse functional IL-2 receptor is a complex comprising three distinct subunits, alpha, beta and gamma chains, but the beta gamma heterodimer is not functional and different from the human heterodimer.