An experiment was conducted to investigate the in-vitro conditions under which coinhibition of viral interferon (IFN) induction occurred when mammalian cell monolayers were exposed to both chrysotile asbestos (12001295) (As) and benzo(a)pyrene (50328) (BaP). Influenza virus (AoPR834) infected rhesus-monkey kidney (LLC- MK2) cell line was exposed to chrysotile As, BaP, and the noncarcinogenic analog of BaP, benzo(e)pyrene (192972) (BeP). The effect on viral IFN induction in the presence of different combinations of chemicals was also studied. An immunofluorescent cell counting assay was used to ascertain the IFN potency of the test samples. Under laboratory conditions, BeP was found to be more cytocidal than BaP. Cells tolerated about a ten fold higher quantity of BaP (0.039 micromole) than BeP (0.0039 micromole) without appreciable loss of viability (less than 0.5 percent). BaP alone was not found to be detrimental to IFN induction. With a mixture of BaP and rat liver S9, inhibitory activity was significantly greater than with any of the reagents tested either alone or in other combinations. The authors concluded that BaP and As (chrysotile form), when used in combination, resulted in coinhibition of viral IFN induction that exceeded the inhibitory action of each of the reagents when tested alone.