An human T-cell leukemia virus (HTLV)-producing cell line (Ra-1) was established from rabbit lymphocytes by co-cultivation with lethally irradiated MT-2 cells. Ra-1 cells were inoculated intravenously into a Japanese monkey and rabbits. All animals responded with the production of antibodies to HTLV. Lymphocytes from the seroconverted animals were grown in the presence of T-cell growth factor (TCGF) or co-cultured with lymphocytes from seronegative healthy persons. The TCGF-grown cells, which were chromosomally of the recipient type, expressed HTLV antigens and particles. The co-cultures gave rise to human T-cell lines which also harbored HTLV antigens and particles. Blood transfusion from the infected rabbits resulted in the seroconversion of the recipient rabbits. HTLV-producing lymphoid cell lines were established from some of the transfused rabbits. The recipient origin of these cell lines was determined by chromosome analysis. It was possible to serially transmit HTLV by blood transfusion in rabbits. Thus, these animals offer promise as a laboratory model for HTLV infection.