Four female rabbits were given twice-weekly oral inoculation of 2-4 X 10(7) cells from a male rabbit lymphoid cell line persistently infected with human T-cell leukemia virus type I (HTLV-I). After 8 weeks, one of them was found to be seroconverted for HTLV-I. Peripheral lymphocytes from the 4 rabbits were cultured in the presence of T-cell growth factor, and a lymphoid cell line with a normal female karyotype was established only from the seroconverted rabbit. This cell line was reactive with a monoclonal antibody to rabbit T-cells and expressed HTLV-I antigens and virus particles.