Administration of the MAO-inhibitor pargyline resulted in an increase of dopamine (DA) and an exponential decrease of the metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in various rat brain areas. From these curves the rate of formation of DA and the rate of removal of DOPAC were calculated, within one experiment, for the striatum, tuberculum olfactorium and frontal cortex. When the accumulation rate of 3-methoxytyramine was taken into account it appeared that the rate of DA formation was in good agreement with the rate of DOPAC removal in the brain areas studied. The contribution of the DA formation to the synthesis of noradrenaline in the frontal cortex appeared negligible. The earlier reported rapid rise of striatal DA levels after administration of aminotetralin-derived DA agonists suggests that the synthesis rate of the biogenic amine is higher than its rate of metabolism. It appeared from the present study that an increased rate of synthesis of DA induced by the DA agonists was responsible for this discrepancy.