Human immunodeficiency virus type 1 (HIV-1) infection is characterized by a gradual loss of CD4+ T cells and T-cell function and an ongoing high level of virus replication. The high replication rate and the error-prone nature of HIV-1 reverse transcriptase create a diverse viral quasispecies throughout infection. To study biological properties of HIV-1 quasispecies in relation to the clinical course of infection, the in vitro preservation of phenotypical characteristics of the virus is essential. Here, we describe the method for bulk isolation of the HIV-1 quasispecies and a limiting dilution virus isolation protocol by which single coexisting HIV-1 variants can be obtained using peripheral blood mononuclear cells from a healthy donor as target cells. In addition, methods for propagation and titration of HIV-1 are provided.