An investigation of the modulation of viral induced enzyme activity in the liver microsomes of mice after exposure via inhalation to coal dust (CD) and diesel exhaust (DE) particulates was conducted by examining two metabolic systems: detoxication through cytochrome-P- 450 (P-450); and resistance to infection through interferon (IFN). White female mice (Swiss-CD1) were exposed using an inhalation chamber for 7 hours per day, 5 days per week to filtered air (FA), CD, or DE. Total particulate levels were 2 milligrams per cubic meter (mg/m3) for DE exposures, and 5mg/m3 for CD exposures. Respirable particulates of less than or equal to 7 micrometers were maintained at 2mg/m3 in both cases. Mice were inoculated with influenza-virus within 24 hours after exposure and during infection, liver microsome samples were obtained and the following enzyme activities were measured: 7-ethoxycoumarin-deethylase (7ECdeEt-ase); NADPH-c-reductase (NADPH-c-red-ase); ethylmorphine-demethylase (EMdeMe-ase). Infection by influenza-virus affected the specific activities of 7ECdeEt-ase and NADPH-c-red-ase as noted by an increased value for both enzymes on day four. Changes in microsomal liver content over the 8 day interval were not observed. Exposure to DE or CD did not result in significant changes in the decreased 7ECdeEt-ase activity observed in control mice (days one to three). The virus induced temporal pattern for EMdeMe-ase in exposed mice was altered. The authors suggested that a relationship exists between P-450 enzyme activity and IFN induction, at least in mice.