Bovine fetal spleen cells synchronized with 2mM hydroxyurea were infected with bovine parvovirus and bovine enterovirus in order to study the events occurring when DNA and RNA viruses mixedly infect single cells. The objectives of this research were threefold. First, to determine the effects of single infection of synchronized bovine fetal spleen cells by bovine parvovirus and bovine enterovirus on cellular macromolecular syntheses. Second, to study the effect of simultaneous infection of synchronized cells by bovine parvovirus and bovine enterovirus. Third, to investigate the interactions which occur when synchronized cells are pre-infected with bovine parvovirus and superinfected with bovine enterovirus. Single infection of cells with bovine parvovirus upon release from hydroxyurea does not affect cellular macromolecular syntheses until 8 hr after infection; whereas, single infection with bovine enterovirus results in a rapid decrease in the rates of total DNA, RNA, and protein synthesis by 2 hr after infection. In simultaneously infected cells, the enterovirus replication is not inhibited while the level of parvovirus is severely reduced. However, in cells pre-infected with bovine parvovirus and super-infected with bovine enterovirus, the replication of both viruses is dramatically decreased. It can be seen from the results obtained in the study of two protocols of mixed infection, that many different virus-host interactions and virus-virus interactions can occur in a mixed infection. The time sequence of infection of the two viruses determines what interactions take place. / Master of Science