Abortive human cytomegalovirus (HCMV) infection of normal hamster cells is accompanied by formation of cytoplasmic and surface receptors for the Fc portion of nonimmune IgG molecules. The process requires RNA and protein synthesis but no DNA synthesis. The surface receptors are detectable only transiently, in a small proportion of the cells. The receptors are also present in cells transformed by HCMV in vitro (87-TRH-5 and CX-90-3B cell lines) as well as in cells of lines TSC-1 and TSC-2 from tumours induced by these cells. Consequently, the indirect immunofluorescence test performed with sera containing no HCMV antibodies may give a positive reaction in the cytoplasm and/or cell membrane of the transformed cells.