The effects of lignite fly ash particulates and soluble components on the interferon system were investigated. The influence of lignite fly ash particulates was studied on viral interferon induction, interferon mediated antiviral cellular resistance, multiplication of influenza virus, and mutagenic activity and effect on interferon production of the soluble components of fly ash. Viral induction of interferon in the presence of fly ash was investigated for the maximal quantity of fly ash that Rhesus-monkey kidney (LLC-MK2) cell monolayers could tolerate without loss of viability. An immunofluorescence cell counting interferon assay was used to determine interferon potency of test samples. Influenza virus replication concomitant with interferon production was measured in fly ash treated and untreated LLC-MK2 cell monolayers. Horse serum, dichloromethane (75092) (DCM), and methanol extracts of fly ash were assayed for mutagenic activity by detecting reverse mutation, from histidine (71001) (HD) dependent to HD independent, of tester strains TA-98 and TA-100 of Salmonella-typhimurium. Presence of fly ash did not impair the ability of exogenous interferon to confer antiviral cellular resistance. Influenza virus multiplication in cell monolayers pretreated with fly ash attained a 2 fold higher rate of growth than normal cell monolayers. Extractions of fly ash by either polar or nonpolar solvents, horse serum with or without ethylenediamine-tetraacetic-acid (60004) (EDTA), and fractionation of serum extracts yielded corresponding extracts antagonistic to viral interferon induction. Residual fly ash particulates after extraction by horse serum with EDTA were capable of inhibiting viral induction of interferon. Neither polar, nonpolar, nor horse serum extracts of lignite fly ash showed mutagenic activity as determined by the Salmonella HD reversion assay. Removal of cell membrane bound sialic-acid (131486) (SA) by neuraminidase or pretreatment of lignite fly ash with SA abolished the adverse activity of fly ash on viral interferon induction. The authors conclude that induction of interferon by influenza virus is depressed by about 50 percent when cell monolayers are pretreated with lignite fly ash.