The metabolic pathway for the formation of adrenaline and noradrenaline has been established, but much remains to be done on the individual reactions. Only two of the reactions in the sequence, the decarboxylation of DOPA and the N-methylation of noradrenaline, have been demonstrated with any clarity of detail. The oxidation of phenylalanine to tyrosine has been studied in other tissues and it is highly probable that the same system applies to the adrenal medulla. The formation of DOPA from tyrosine has been found to be catalyzed by tyrosinase both in invertebrates and in mammalian tissues and it is likely that this enzyme may also be found in the adrenal medulla. The reaction in which noradrenaline is formed from hydroxytyramine is the least understood of the entire sequence. Initial studies indicate that this reaction is complex but show promise of elucidation.