Accurate measures of inhibition of virus replication are needed to evaluate the efficacy of antiretroviral agents in large clinical trials. We describe an accurate, economical and rapid method for the direct detection and quantification of cell-free human immunodeficiency virus type -1 (HIV-1) in serum or plasma. The method includes affinity capture of the virus by latex microparticles coated with HIV-1 envelope-specific antibodies, reverse transcription primed by an HIV-1 specific oligonucleotide and amplification by nested PCR of the synthesised cDNA. We show that the method can be applied to large numbers of serum samples, is reproducible and is highly applicable to the monitoring of viral load in HIV-1 infected patients, especially during the investigation of drug efficacy.