The organization of the mitotic apparatus was studied in human embryo lung fibroblasts (HEL) and Vero cells at 4 days postinfection with human cytomegalovirus (HCMV) strain AD 169. The bipolar spindle was detected by immunofluorescence in p72-positive mitotic cells exhibiting a regular or C-metaphase-like chromosome configuration. Electron-microscopic study of C-metaphase-like cells revealed alteration of the centrosome structure which is characterized by the following features: (1) breakdown of the diplosome, (2) separation of the fibrillar material from centrioles, and (3) disruption of the centriolar cylinder. The spindle pole in the aberrant mitotic cells consisted of one or several foci of microtubules converging on the fibrillar aggregates. There are not any signs of the nuclear envelope reconstruction found in mitotic cells with highly condensed scattered chromosomes. Unlike in HEL cells, viral particles were not detected in Vero cells. A question arises as to whether centrosome injury is an integral part of the events leading to cell death unrelated to the reproduction of HCMV.