There exists considerable evidence that the growth of glial cells can be influenced by T-cell-derived lymphokines and monokines. Astrocytes proliferate in the presence of mitogen- or antigen-stimulated T-cell supernatants, supernatants from human T-lymphotropic virus (HTLV)-transformed T cells, and purified human interleukin-1 (IL-1; ref. 4). Oligodendrocytes proliferate and differentiate when incubated with supernatants from mitogen-activated or HTLV-transformed T cells. In addition, we have recently purified a T-cell-derived lymphokine of relative molecular mass 30,000, termed glial growth promoting factor (GGPF), which specifically stimulates the proliferation of oligodendrocytes. The traditional role of interleukins 1 and 2 is in the initiation, propagation and regulation of the immune response. IL-1, released by a variety of cells including monocytes, stimulates T cells to produce IL-2; IL-2 in turn induces the expansion of T cells that is critical for immune responsiveness. Recently, IL-2 has been shown to induce B-cell proliferation and immunoglobulin secretion, indicating that its action is not restricted to T cells. We now report that recombinant human IL-2 influences the growth of glial cells--specifically, the proliferation and differentiation of oligodendrocytes. IL-2 may have a role in the inflammatory neural lesions of multiple sclerosis patients and in the growth of brain glia during injury or disease.