The accumulation of virus-specific early RNA in mouse 3T6 cells infected by wild type polyoma virus or by a tsA mutant, tsA25E, was measured by hybridization of cytoplasmic RNA to radiolabeled "early" strand polyoma DNA. Cells infected by the tsA25E mutant accumulated approximately 20 times more virus-specific early RNA during the early phase of lytic infection than did wild type-infected cells at both the permissive and the nonpermissive temperature under identical conditions of infection and hybridization. Cells infected by the tsA25E mutant at the permissive temperature continued to accumulate virus-specific early RNA during the late phase of infection after being shifted to the nonpermissive temperature to block further viral DNA replication. A mixed infection of cells by wild-type polyoma and tsA25E showed that the overproduction of early RNA by the tsA mutant alone could be suppressed by coinfection with the wild type. The results suggest that the A gene product of polyoma regulates transcription of early RNA, as has been suggested for SV40 (Reed et al., 1976) and that the wild-type A-gene product overcomes the effect of the temperature-sensitive A-gene product.