The effect of bcl-2 expression on cell viability and recombinant protein synthesis was investigated in the Spodoptera frugiperda Sf-9 and Trichoplusia ni BTI-Tn-5B1-4 (High Five(TM)) insect cell lines. It was found that coinfection with a baculovirus expressing bcl-2 [Autographa californica nuclear polyhedrosis virus (AcNPV)-bcl2] extended the life span of High Five(TM) cells but not Sf-9 cells when compared to infection with recombinant baculoviruses expressing either human tissue plasminogen activator (AcNPV-tPA) or Escherichia coli beta-galactosidase (AcNPV-beta gal). Similar results were obtained in coinfection experiments; i.e., AcNPV-bcl2 coinfection increased the life span of High Five(TM) cells over that of cells infected with either AcNPV-tPA or AcNPV-beta gal alone, but they did not affect the lifespan of coinfected Sf-9 cells. Coinfection of Sf-9 cells with AcNPV-bcl2 and AcNPV-beta gal resulted in a decrease in the maximum beta-gal expression levels of over 90% when compared to infection with AcNPV-beta gal alone. A similar trend was found in the beta-gal mRNA levels. Coinfection also resulted in a reduced beta-gal expression level in High Five(TM) cells, but the reduction was consistent with what would be expected when two recombinant viruses compete far use of the cellular machinery. In contrast to the inhibitory effect of AcNPV-bcl2 coinfection on beta gal expression, t-PA expression levels were either not affected (Sf-9 cells) or were increased 50% (High Five(TM) cells) over those obtained by infection with AcNPV-tPA alone. These results support the hypotheses that bcl-2 can inhibit transcription of genes under polyhedrin promoter control and that beta-gal expression levels, but not t-PA expression levels, are controlled at the transcriptional level.