The effects of food deprivation, carbohydrate restriction and ethanol consumption on the metabolism of eight volatile hydrocarbons (benzene, toluene, styrene, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene and trichloroethylene) in rats were compared with the effects of enzyme induction by phenobarbital (PB), polychlorinated biphenyl (PCB) and 3-methylcholanthrene (MC) on the metabolism of these compounds. Although causing a marked increase both in microsomal protein and cytochrome p-450 contents, PB (80 mg/kg per day for three days) and PCB (a single dose of 500 mg/kg) induced only a limited range of enzyme activity: PB increased the metabolism of toluene, styrene, chloroform, carbon tetrachloride and trichloroethylene, and PCB only increased those of toluene, styrene and trichloroethylene. MC (20 mg/kg per day for three days) had no effect on the metabolism of any of the hydrocarbons studied. In contrast, food deprivation, carbohydrate restriction and three-week ingestion of ethanol (2.0 g/day), each enhanced the metabolism of all the hydrocarbons with little or no increase in microsomal protein and cytochrome P-450 contents. PB, PCB and MC treatments enhanced the activity of enzymes involved in conjugation reactions, UDP-glucuronyltransferase and glutathione S-transferase, whereas the dietary manipulation and ethanol consumption produced no significant effect on these enzymes. It is concluded that ethanol consumption. lowered carbohydrate intake and food deprivation affect the metabolism and toxicity of volatile hydrocarbons differently from PB, PCB or MC.