A total of 56 sera from asymptomatic HIV-seropositive subjects and patients with symptomatic HIV infection were studied by immunoblotting for IgM, IgG and IgG subclass reactivity against cytomegalovirus structural polypeptides. The results showed a high percentage of IgM-positive sera in the asymptomatic patients, and IgM reactivity was particularly high against a polypeptide of intermediate molecular weight (p66). IgG reactivity was very high against the majority of viral structural polypeptides with the possible exceptions of p82 and p61, in all patients. Antibody to these polypeptides decreased with the increase in HIV-specific symptoms. No significant difference in the reactivity of IgG subclass to viral polypeptides was found among the different groups of subjects, except for a generalized increase in IgG subclass reactivity from asymptomatic to HIV-specific symptomatic patients.