The first half of this report describes direct evidence for the interleukin 2 receptor (IL-2R)-inducing ability of human T-cell leukemia/lymphoma virus (HTLV). When an Epstein-Barr virus (EBV)-transformed human B-cell line, LCL-Kan was infected with HTLV or transfected with plasmid DNA containing defective HTLV genome (long terminal repeat (LTR)-gag-pX-LTR), LCL-Kan cells were altered to express IL-2R which was indistinguishable from that of normal activated T cells. The second half of this paper reports that IL-2 could inhibit proliferation of HTLV-carrying T-cell lines which were spontaneously immortalized from IL-2-dependent cells or peripheral blood cells containing ATL leukemia cells. These results suggest that expression of IL-2R may be induced by HTLV in HTLV-transformed cells, where the IL-2R plays an important role in transduction of continuous cell growth signal.