A DNA fragment containing the tat , rev and env genes of the human immunodeficiency virus type 1 was inserted into the retroviral vector pZIP neo AU3. The resulting plasmid p env AU3 was transfected into HeLa and ψCRIP cells. Resulting recombinant retroviruses were used to infect HeLa and Jurkat cells. Immunoprecipitation analysis of stable transformants showed the expression of HIV env glycoproteins gp160, gp120 and gp41. Transactivation assays with a plasmid containing the gene for chloramphenicol acetyltransferase linked to HIV promoter-enhancer sequences demonstrated the expression of functional tat . These cells constitute virus-free tools for functional and structural studies of native env and tat .