HIV-1 Env pseudotyped viruses (PV) are an attractive tool for studying the antiviral activities of compounds interfering with virus entry into a target cell. To investigate whether results obtained in PV assays are relevant biologically, the antiviral activity of 6 reference compounds was compared on 5 virus isolates of different clades using three assays: (1) replicating virus in peripheral blood mononuclear cells (PBMCs), (2) PV in CD4 and CCR5- or CXCR4 co-receptor expressing Ghost cells, and (3) PV in PBMCs. A significant linear relationship was found between both single-cycle PV assays (P <0.0001, R 2 =0.75). Moreover, both assays showed enhanced sensitivity to the antiretrovirals tested (P =0.013 and 0.015, respectively) as compared to the PBMC assay with replication-competent virus. Most importantly, results from the latter assay could be predicted significantly from both PV assays, in which either Ghost target cells (P <0.0001, R 2 =0.61) or PBMCs (P <0.0001, R 2 =0.55) were used. The usefulness of the PV assay was demonstrated further by investigating the impact of the HIV-1 Env subtype on the antiviral activity of five new compounds derived from the entry inhibitor BMS806.