To determine the susceptibility of rabbits to experimental infection with human T-cell lymphotropic virus type-II (HTLV-II), four separate groups of four weanling rabbits each were inoculated intravenously with lethally irradiated HTLV-II-infected human cell lines Mo-T (HTLV-IIMo- infected T cells), WIL-NRA (an Epstein-Barr virus [EBV]-transformed B- lymphoblastoid cell line infected with HTLV-IINRA), 729pH6neo (an EBV- transformed lymphoblastoid cell line transfected with a molecular clone of HTLV-IIMo), or G12.1 (HTLV-II-infected T cells from a Panamanian Guaymi Indian). Two additional groups of four rabbits each were similarly inoculated with control uninfected 729 or HuT 78 cells. Early and persistent seroconversion to HTLV-II core antigen p24, as determined by Western immunoblot, occurred in all HTLV-II-inoculated rabbits and was most intense in rabbits inoculated with G12.1 cells; seroreactivity to other HTLV-II gag or env antigens occurred later, with less intensity, or not in all inoculated rabbits. Peripheral blood mononuclear cells (PBMC) and other lymphoid cells from HTLV-II- inoculated rabbits produced minimal p24 in vitro, as determined by enzyme immunosorbent capture assay. Virus was more readily detected by polymerase chain reaction amplification of HTLV-II pol sequences; this occurred most frequently in rabbits inoculated with Mo-T cells, and most frequently in PBMC as compared with other tissues tested (bone marrow, brain, and liver). No evidence of disease occurred in HTLV-II- inoculated rabbits observed for as long as 24 weeks. All control rabbits remained negative for evidence of HTLV-II infection, as determined by the same procedures. These results provide the first evidence of HTLV-II infection in a species other than humans, and demonstrate the usefulness of the rabbit as an animal model to study the biologic response to different isolates of this human retrovirus.