Adeno-associated virus is a nonpathogenic, dependent parvovirus that integrates at a specific site in human chromosome 19. We have used the inverted terminal repeats of the virus, which mediate integration, to establish a vector for gene transfer in human lymphocytes. A neomycin resistance gene has been stably introduced into nontransformed human T-cell clones and a subsequent analysis of the functional properties of the infected clone revealed no detectable alterations. Rescue and replication of the wild-type virus was accomplished with adenovirus superinfection; however, the vector was not rescued and did not replicate by this procedure, indicating the stability of the integrated vector and demonstrating an additional level of safety incorporated in its construction. An adeno-associated virus-based vector represents an alternative to retroviruses for gene therapy in lymphocytes.