Synthesis of proteins and RNA's specified by human cytomegalovirus are being studied in permissive and nonpermissive cells. These viral gene products are being classified as immediate early, early, or late. Permissive cells allow for the synthesis of all three classes of gene products. Nonpermissive cells permit only a limited expression of the viral genome. These cells are being analyzed to determine which early viral proteins and RNA's are synthesized. The nonpermissive cell is being used as a type of cell that favors latency of the CMV genome. Presence of the viral genome in nonpermissive cells or permissive cells in which replication of the viral DNA is blocked is being quantitated by DNA:DNA reassociation kinetics.