A hyperimmune plasma collected from healthy, HIV-1 infected individuals with high titers of neutralizing antibodies was administered to 7 AIDS and 3 ARC patients. 500 ml of plasma was administered monthly for 10 months. All patients were monitored for viral antibodies, antigen and ciral nucleic acid by PCR. DNA and RNA-PCR was performed on nucleic acid isolated from serum using primers from the gag region of the HIV-1 genome. HIV-1 DNA and RNA were detected prior to administration of immunoglobulin in all patients. No viral nucleic acid could be detected in serum after the first transfusion in any patient and this remained so for the length of the study in ARC patients. Viral sequences were detected in 3/7 AIDS patients towards the end of the trial (10-11 months). HIV antigen was not detected, except in 2 AIDS patients towards the end of the trial. These results indicate that hyperimmune plasma eliminated detection of HIV nucleic acid from the plasma of both AIDS and ARC patients although the effect was not as sustained in AIDS. Passive immunization may be useful in clearing plasma viremia, particularly in ARC patients. In a prospective study, serum and cells from 50 patients enrolled in a controlled study for evaluation of the therapeutic value of hyperimmune plasma, are being analyzed by PCR for HIV DNA and RNA.