Metabolism of vincamine has been studied in rats in vivo and in vitro using tritium labelled vincamine. Radioactivity was excreted with urine and faeces in an amount of about 62% during 72 h after i.v., i.p. and p.o. administration of the drug. From bile about 40% radioactivity could be recovered during 6 h following i.p. administration. Vincamine is excreted in unchanged form in an amount of 4-6%. In an in vitro system containing rat liver homogenate 6 alpha- and 6 beta-hydroxy-vincamine are formed, as their structures could be deduced from the mass spectrometric data. Rat plasma probably hydrolizes vincamine to vincaminic acid, but the presence of vincaminic acid could not be demonstrated, neither in urine nor in bile. Mass spectrometric investigations of the urinary and biliary metabolites have shown that beyond 6 alpha- and 6 beta-hydroxy-vincamine, their further oxidized form, 6-keto-vincamine also appears. 6 alpha-, 6 beta-hydroxy-vincamine, 6-keto-vincamine and vincamine are eliminated with urine and bile in part as conjugates. Among the metabolites (+)-eburnamonine (vincamone) was also found, which is supposed to be the degradation product of vincaminic acid. The identified compounds are responsible for about 70% of urinary and 30% of biliary radioactivities.