The effect of reversible inhibitors of the monoamine oxidase type A (MAO-A), moclobemide (Aurorix) and Ro 41-1049 (20 mg/kg i.p. each), as well as of reversible inhibitors of the MAO type B (MAO-B), Ro 19-6327 (1 mg/kg i.p.), on the outflow of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) was studied in the rat by transstriatal microdialysis. Reversible MAO-A inhibitors markedly increased the output of DA and concomitantly decreased the output of DOPAC and HVA. These effects were absent with the highly selective MAO-B inhibitor Ro 19-6327.