Monocytes from healthy blood donors were inoculated in vitro with a monocyte-tropic strain of human immunodeficiency virus type 1 HIVBa-L. HIV replication was first detected at Day 5 postinoculation, with peak virus activity at Day 17. We assessed the kinetics of the expression of four monocyte surface antigens (CD14, CD4, HLA-DR, and HLA-DQ) on HIV-infected and uninfected monocyte/macrophages, (M phi) by flow cytometry. We consistently found a decreased expression of CD4 and CD14 on HIV-infected M phi compared to their expression on M phi of uninfected controls. In contrast, HLA-DR and HLA-DQ expression was unchanged on HIV-infected M phi.