The metabolism of [3H]dopamine injected into the lateral cerebroventricles, was studied in rats after treatment with either ethanol or chloral hydrate. The experimental system was designed primarily to detect the possible conversion of dopamine to the tetrahydroisoquinoline derivatives, tetrahydropapaveroline, salsolinol and O-methylsalsolinol. With or without pretreatment with ethanol or chloral hydrate, no conversion of [3H]dopamine to [3H]tetrahydroisoquinolines was detected. The limits of detection per rat brain were: tetrahydropapaveroline < 1.6 × 10-14 moles (0.00032% conversion), salsolinol < 1.6 × 10-13 moles (0.00032% conversion), and 6- and 7-O-methylsalsolinol < 3.2 × 10-14 moles (0.00032% conversion). Two consistent ethanol- or chloral hydrate-induced alterations in [3H]dopamine metabolism were noted: (1) small but statistically significant increases in the ratios of reduced to oxidized metabolites resulting from monoamine oxidase action; and (2) decreased relative amounts of N-methylated metabolites.