Expression of the gamma chain, which is shared among functional receptor complexes for interleukin (IL)-2, IL-4 and IL-7, was examined with hematopoietic cells in mouse thymus and spleen by flow cytometry. The gamma chain was expressed in cell populations from the spleen. Stimulation with concanavalin A and lipopolysaccharide caused fluctuation in expression of the gamma chain in T and B cells, respectively. T lineage cells developing in the adult thymus expressed the gamma chain. Fetal thymus at day 15 contained mostly immature thymocytes, which also expressed the gamma chain. These results demonstrate that the gamma chains is widely expressed in T lineage cells, probably indicating that the gamma chain plays a role not only in the proliferation of mature hematopoietic cells but also in the development of immature cells through signal transduction as a common receptor subunit for multiple cytokines.