Stimulation of a class II-restricted, antigen-specific T cell clone with interleukin 2 (IL-2) resulted in substantial increases in both cell surface IL-2 receptor (IL-2-R) and cytoplasmic IL-2-R messenger RNA (mRNA), whereas no increase was observed for cell-surface expression of Thy-1 and L3T4 antigens, and only a modest increase in Thy-1 mRNA was observed. These experiments demonstrate that, after initial acquisition of the IL-2-R, IL-2 as well as antigen is able to directly upregulate both the level of IL-2-R mRNA and cell surface IL-2-R molecules.