1,2-Dihydro-2,2,4-trimethylquinoline (TMQ), an antioxidant used in the rubber industry, was readily absorbed from the gastrointestinal tract of the male Fischer 344/N rat and rapidly distributed throughout the body tissues. Absorption, distribution, metabolism, and excretion were not significantly affected by dose in the range 11.5-1150 mumol/kg. Following iv administration, the greatest amounts of TMQ-derived radioactivity were present in the high volume tissues including muscle, adipose, skin, liver, and blood. TMQ had no particular affinity for any tissue. TMQ-derived radioactivity was excreted primarily in urine (60-70%) and feces (20-30%) within 3 days after administration. Greater than 99% of the TMQ dose excreted in urine and feces was in the form of metabolites. Urine contained two major and ten minor metabolites while feces contained two major and four minor metabolites. The two major TMQ metabolites in urine were identified by NMR and mass spectroscopy as the O-sulfate conjugate of 1,2-dihydro-6-hydroxy-2,2,4-trimethylquinoline and the monosulfate conjugate of 1,2-dihydro-1,6-dihydroxy-2,2,4-trimethylquinoline. In vitro studies with liver subcellular fractions suggest that most of the metabolites present in urine, feces, and bile are the products of mixed function oxidase activity and conjugates of these metabolites. Multiple exposure of rats to high TMQ doses (1150 mumol/kg) resulted in some bioaccumulation of TMQ-derived radioactivity in all tissues examined, but these residues did not persist when dosing was discontinued.