The T-cell tropic primate herpesviruses, Herpesvirus saimiri (HVS), and the T-cell tropic RNA tumor viruses, human T-cell leukemia virus (HTLV), have both recently been shown by us and others to transform (immortalize) primate and human T-cell in vitro. Transformed cell lines were developed from the peripheral blood cells of an individual marmoset by HVS, HTLV, and by cocultivation with HVS and HTLV. These cell lines as well as several HVS-transformed owl monkeys cells are positive for the E-rosette receptor and reactive with a pan-T-cell monoclonal antibody. In contrast to normal T-cells, they do not require added interleukin-2 (IL 2) for growth. An IL-2 specific cDNA probe which hybridizes to RNA from normal PHA-treated primate lymphocytes failed to hybridize to RNA from either HVS or HTLV-transformed marmoset or owl monkey T-cells. The addition of purified IL 2 to HVS-transformed cells stimulated a 2-to 5-fold increase in cell growth while it had no effect on the growth of HTLV-transformed cells. IL 2 receptors were studied by binding of biosynthetically-labeled (3H)-IL 2 to cells and by immunofluorescence binding of anti-TAC, a monoclonal antibody to the IL 2 receptor, as measured by flow cytometry. Results on IL 2 receptor studies indicated that: 1) IL 2 receptors on both HVS and HTLV transformed cells did not cycle on and off the plasma membrane as in normal T-cell growth and 2) HVS-transformed T-cells had normal levels of IL 2 receptors while the receptor density on HTLV-transformed T-cells was 8- to 10-fold higher. Scatchard analysis was consistent with the presence of one class of high affinity receptors on HVS-transformed cells. The addition of purified natural or recombinant IL 2 increased the level of receptors 2-to 3-fold after 24 hrs on HVS-transformed cells but had no effect on receptor density on normal or HTLV-transformed cells. The transferrin receptor also appeared to be upregulated by IL 2 on HVS-transformed cells but two other surface receptors were not. The T-cells co-infected with HVS and HTLV have the phenotype of HTLV-transformed cells. These results indicate that IL 2 receptor physiology varies among transformed T-cells.