The vif gene of HIV-1 has previously been claimed to be essential for the ability of cell-free virus preparations to infect cells. Here we report that the CEM T-cell-line, stably transfected with and expressing vif, supports the replication of vif- HIV-1 viruses to the same extent as wild-type HIV1. Cell entry and early replication stages are the same for vif- and vif+ HIV-1 passaged in CEM, as measured both by a PCR-based cell entry assay and by fusogenic potential. These findings indicate that vif does not affect viral infectivity on CEM cells, but seems to act at a later stage of virus replication/maturation. We also show that the VIF proteins of two different HIV-1 strains can transcomplement different vif- HIV-1 mutants.