Highly-sensitive and reproducible method is developed for simultaneous assay of noradrenaline, dopamine, serotonin and 5-hydroxyindolylacetic acid in small samples of brain tissue. The procedure comprised extraction of the substances with acidified butanol, reextraction of the compounds with phosphate buffer in presence of isooctane, separation of the amines form precursors and metabolites using ion exchange resin Amberlite CG-50 and of 5-hydroxyindolylacetic acid--on Sephadex G-10.