Activation and metabolism of xenobiotics by rat nasal tissue were studied in-vitro. Nasal tissue (the maxilloturbinates, ethmoturbinates, and nasal epithelial membrane) isolated from male F344-rats, some of which had been pretreated with phenobarbital (50066), 3-methylcholanthrene (56495) (MC), Aroclor-1254 (11097691), or 2,3,7,8-tetrachlorodibenzo-p-dioxin (1746016) (TCDD) were assayed for aryl-hydrocarbon-hydroxylase (AHH), epoxide-hydrolase, uridine-5'-diphospho-glucuronyltransferase (UDGPT), and glutathione-transferase (GSHT) activities. Benzo(a)pyrene (50328) (BaP) and 1-nitropyrene (5522430) (nitropyrene), styrene-oxide (96093), 7-hydroxycoumarin (93356), and styrene-oxide were used as substrates, respectively. The nasal tissue S9 fraction was isolated and tested for its ability to alter the mutagenicity of BaP and nitropyrene in the Ames Salmonella assay with strains (TA-98), (TA-100), and (TA-98NR). Parallel experiments were carried out with lung and liver homogenates for comparison purposes. Specific enzyme activities in rat nasal tissue expressed as nanomoles of product per milligram protein per minute were as follows: AHH, 0.02 with BaP as substrate and 0.68 with nitropyrene as substrate; epoxide-hydrolase, 6.4 with styrene-oxide as substrate; UDPGT, 20.4 with 7-hydroxycoumarin as substrate; and GSHT, 24.8 with styrene-oxide as substrate. Rat nasal tissue metabolized BaP to dihydrodiols, quinones, and phenols and nitropyrene to phenols. BaP was metabolized by liver tissue at a rate 5 to 50 times greater than in lung tissue and about 12 times greater than in nasal tissue. Nitropyrene metabolism occurred at a much higher rate in nasal tissue than in liver or lung tissue. TCDD pretreatment caused a twofold increase in nasal metabolism of BaP. Phenobarbital, MC, and Aroclor-1254 had no effect on BaP metabolism. Nasal, lung, and liver tissues bioactivated both BaP and nitropyrene to mutagenic products. Nitropyrene consistently showed more mutagenic activity than BaP. The authors conclude that rat nasal tissue contains oxidative and nonoxidative enzymes capable of metabolizing xenobiotics to mutagens. Rat nasal tissue may be important in determining the metabolic fate of inhaled xenobiotics.