Thirty patients with AIDS-related complex/Walter-Reed 5 enrolled in a placebo-controlled double-blind study with high-dose intravenous gammaglobulin administration were tested by quantitating HIV Western blot and other serological tests for viral antibodies. Furthermore, conventional virus isolation attempts were performed. Absence or loss of p24 antibodies during the study period was associated with progression to AIDS (p = 0.01) and thereby was an earlier prognostic parameter of a poor prognosis than T4 cell count. Neither changes in antibody patterns against other HIV polypeptides, HIV titers in the immunofluorescence test nor demonstration of HIV antigen were significantly associated with progression to AIDS. Cytomegalovirus (CMV) could be isolated from two duodenal biopsies of a patient who developed AIDS at the same time, but a concomitant serological diagnosis of CMV infection was not successful. Though signs in the serology of human herpesviruses (herpes simplex virus, CMV, Epstein-Barr virus), possibly indicating a reactivation of latent infections, could be observed in some instances, a correlation with clinical symptoms or the clinical outcome was not feasible, perhaps also because of a poor standardization of some of the test kits used. All patients were positive for IgG antibodies against the three herpesviruses when entering the study. High prevalence of hepatitis B virus (HBV) markers was found (83% anti-HBc positive), only 1 patient being chronically infected and highly infectious, as shown by HBV-DNA hybridization. No significant difference between treatment and placebo group was observed with the parameters tested in this study.