Cell cultures of embryonic calf kidney which had been infected with bovid herpes virus 2 were examined for cytological and histochemical changes. The morphological changes recorded from cells damaged by virus infection included the formation of gigant syncytial cells and intranuclear inclusions of Cowdry Type A. The cytological changes in the infected cells were accompanied by variation in enzyme activity. Recordable were rise in lactate dehydrogenase and alkaline phosphatase as well as decline in succinate dehydrogenase and acid phosphate activity. These phenomena were found to have resulted from impediment of cell metabolism by virus action.