At the time when this investigation was being considered (June, 1961) the efficacy of the monoamine oxidase inhibitors in the treatment of depressive illnesses was already well recognized. It was also evident from a study of the published papers on this group of drugs that their use was accompanied by a number of side-effects which often raised problems in treatment. The clinical trial of a new drug of this class which, from the pre-clinical toxicity studies in animals, held promise of being less toxic than M.A.O. inhibitors already in clinical use was therefore considered worth while. Such a trial also seemed a useful opportunity to follow up previous observations with phenelzine (Gilmour, 1960) and the suggestion of Sargant (1961) that, given concurrently, M.A.O. inhibitors may potentiate the effect of E.C.T. and reduce the number of exposures necessary, and that their continuance after a course of E.C.T. has been completed may reduce the relapse rate.