Investigations of human immunodeficiency virus (HIV) infection of man have benefited from the study of relevant animal models of the infection and disease. However, the ultimate models use primate species which are either endangered, not generally available, or expensive to maintain. A transgenic rabbit specifically and stably expressing human CD4 protein on T lymphocytes was assessed as a new laboratory animal model for HIV-1 infection. In vitro studies demonstrate that lymphocytes derived from the transgenic rabbits are more susceptible to HIV-1IIIB infection than those from normal rabbits. In vivo infection of huCD4-transgenic rabbits using HIV-1IIIB-infected autologous lymphocytes was demonstrated by virus isolation, detection of HIV-1-specific DNA in peripheral blood lymphocytes and seroconversion to various HIV-1 proteins. Viral DNA was detected in the tissues of one rabbit sacrificed 7 weeks post-infection and virus was isolated from lymph node. Although these transgenic rabbits are less sensitive to HIV-1 infection than man, such a small and inexpensive animal model may be a useful tool.