Using polyethylene glycol (PEG) precipitation we have found that most HIV-1 seropositive patients have IgG containing-circulating immune complexes (CIC). In addition these CIC sometimes contain IgA, IgM, C3, and/or HIV p24 antigen. Previous work has demonstrated that patients who have plasma viremia, CD4 cell counts less than 170/mm3, or who are symptomatic are more apt to have HIV that is precipitable with PEG. In this study we report that the infectious HIV found in the plasma of patients with plasma viremia could only be found in the 2% PEG precipitates, i.e., PEG supernatants never contained infectious HIV, although they often contained noninfectious p24 antigen. These results suggested that at least some of the infectious HIV circulating in the plasma of infected patients is in the form of immune complexes. To support this idea we also demonstrated that infectious HIV could be precipitated with antiserum raised to either immunogloblins or complement components.