Phagocytic phenomena have been reported in cultures of fibroblast cells infected with cytomegaloviruses isolated from humans, ground squirrels, and dogs. The rate and amount of phagocytosis were significant, and both the host cells and the engulfed cells had intranuclear inclusions typical of infection with cytomegalovirus. The ingested cells frequently survived within the phagocyte and combined with it to form giant, multinucleated structures that still retained active ingesting ability. These findings in vitro suggest that phagocytes may contribute to the persistence and dissemination of cytomegaloviruses in vivo and that the capacity of certain strains to promote phagocytosis may influence the macrophage-dependent reactions of the host.