Infection of human T cells by human T-lymphotropic virus, type I (HTLV-I), a retrovirus, is uniformly associated with the constitutive expression of large numbers of cellular receptors for interleukin-2 (IL-2). Comparison with normal T cells shows that neither IL-2 receptor gene organization nor IL-2 receptor messenger RNA processing are altered in the leukemic cells. However, mitogenic stimuli activate IL-2 receptor gene expression in normal T cells, whereas these stimuli paradoxically inhibit IL-2 receptor gene transcription in HTLV-I-infected leukemic T cells.