The effects of diesel exhaust, coal dust, and n-alkanes on lung and liver enzymes were studied in rats. Male Fischer-344-rats were exposed by inhalation to 1 milligram per cubic meter (mg/m3) diesel exhausts or 1mg/m3 coal dust alone or in combination 7 hours daily, 5 days per week for 2 years. Cytochrome-p-450 associated benzo(a)pyrene-hydroxylase (BaP hydroxylase) and 7-ethoxycoumarin-o-deethylase activities were assayed in lung and liver microsomes after 3, 6, or 24 months. Sprague-dawley-rats that had been pretreated with 0 or 80mg per kilogram beta-naphthoflavone (6051872) (BNF) were exposed to 0 to 2 millimolar (mm) concentrations of six straight chained alkanes. Enzyme activities in lung and liver microsomes were determined. Diesel exhausts plus coal dust caused a slight, statistically insignificant, reduction in lung BaP hydroxylase activity. No other changes in lung and liver activities were observed. In non BNF pretreated rats, liver enzyme activities were decreased by 2mm alkanes, maximal decreases of 79 and 72 percent, respectively, occurring with n-octane (111659). Lung enzyme activities were not affected. In BNF pretreated rats, lung o-deethylase activity was decreased by 44 percent by n-octane. The author concludes that enzyme sensitivity depends on the alkane.