Radioiodinated normal rabbit IgG was used to detect Fc receptors on the surface of HeLa S3-2 cells infected with herpes simplex virus (HSV). Unlike the Fc receptors present on most leukocytes, these virus-induced Fc receptors were found to be sensitive to trypsin at concentrations of enzyme as low as 0.1 mg/ml. Treatment of infected cells with neuraminidase enhanced the binding of IgG. Yet the HSV-induced Fc receptor(s) is probably a glycoprotein because its synthesis was inhibited by 2-deoxy-D-glucose at concentrations inhibiting glycoproteins but not total proteins. Binding of radioiodinated IgG to Fc receptors on infected HeLa S3-2 cells was unaffected by F(ab′)2 fragments prepared from antisera against uninfected HeLa S3-2 cells or against human β2-microglobulin. By contrast, anti-HSV F(ab′)2 or Fab′ fragments decreased binding of radioiodinated IgG to HSV-infected cells by 85%, and binding of radioiodinated Fc was also inhibited by anti-HSV Fab′.