The IgG subclass pattern against linear antibody binding sites on glycoproteins of human cytomegalovirus (HCMV) was investigated in HCMV-positive healthy blood donors, human immunodeficiency virus-infected persons, sera from mothers with primary HCMV infection during pregnancy and their children, and sequential sera from transplant recipients. As antigens, three immunodominant domains capable of inducing neutralizing antibodies during natural infection were selected on glycoproteins gp58/116 (gB) and gp86 (gH). Bacterial fusion proteins representing these regions were used as antigens in a subclass-specific ELISA. Reactivity against the antibody binding site on gp86 was detected in both the IgG 1 and IgG3 subclasses. In contrast, exclusively IgG1 antibodies were found against both linear domains on glycoprotein complex gp58/116 and also against full-length gp58/116 expressed in insect cells. The data demonstrate a differential regulation of the antibody response to envelope components of HCMV. © 1994 by The University of Chicago.