We established a method to estimate the amounts of HIV-1 particles in plasma from patients with HIV-1 infection by using polymerase chain reaction (PCR) following reverse transcription (RT) of viral RNA (RNA-PCR) and assessed the potential usefulness of this approach to monitor the changes of viral load in patients with AIDS or AIDS-related complex (ARC) receiving 2',3'-dideoxyinosine (ddI). Plasma samples were obtained from 77 patients with HIV-1 infection (49 AIDS/ARC and 28 asymptomatic seropositives). Following ultracentrifugation of plasma, RNA was extracted from the pelleted virus and subjected to RT and PCR. The number of HIV-1 virus particles in each sample was determined using known amounts of HIV-1 DNA as reference control for PCR. The current plasma RNA-PCR technique quantitatively detected HIV-1 particles in plasma from 76 of 77 (98.7%) HIV-1-infected individuals examined. The numbers of HIV-1 particles in plasma from patients with AIDS or ARC were markedly higher than those in plasma from asymptomatic seropositive individuals (p less than 0.0001). Higher levels of plasma HIV-1 particle numbers were detected in individuals with lower CD4+ T cell counts. Patients (n = 10) who received oral ddI at doses greater than or equal to 6.4 mg/kg/day for 8 to 14 weeks had a profound decrease in plasma HIV-1 particle numbers (p = 0.0051). Patients (n = 7) receiving ddI for 45 to 71 weeks also had a decrease (p = 0.018). It should be noted, however, that more research is required to evaluate the usefulness of this technique in assessing the disease status and monitoring the activity of antiretroviral therapy.