S u , , n a r y Rabbit kidney epithelial cells (RK13) exhibited a cytopathic effect (CPE) characterized by celt rounding after infection with human eytomegalovirus (HCMV). Although HCMV-specific immediate early and early antigens were detected by indirect immunofluoreseence techniques, neither tare antigens nor infectious progeny virus could be observed in virus-infected 1~K13 cells. HCMV-infected RKls cells showed a prolonged doubling time and a decreased saturation density in cell growth compared to uninfected control cells. Moreover, colony forming ability (CFA) of virus-infected cells decreased by approximately 70 per cent compared to that of uninfected cells during the first 24 hours after infection. These results indicate that an abortive infection of RK~s cells with HCMV induces an alteration of growth pattern including morphological changes with cytocidal effect. .In general, infection of nonhuman cells with human eytomegalovirus (HCMV) results in the production of infectious virus to a limited degree (16) or an abortive infection (1, 7). In these virus-infected nonhuman cells, characteristic morphological changes are frequently induced and some, if not all, immediate early and early virus proteins and antigens are detectable (t, 3, 6). In addition, although no viral DNA synthesis occurs in nonhuman cells, an abortive infection can stimulate cellular DNA synthesis (4, 9, 12).