Cyclizine hydrochloride (1-benzhydryl-4-methylpiperazine monohydrochloride) is a popular remedy for motion-sickness. The success which is reputed to attend the use of the drug in this condition may be a function of of two distinct effects: (a) a direct, specific inhibition of the vestibular mechanism; (b) a general, central inhibition or sedation. A consideration of the latter, rather than the former, suggested the possibility that cyclizine might prove to be of value as a potential “tranquillizer”. A controlled clinical trial was carried out in order to establish whether any tranquillizing effects might be associated with the use of the drug in a number of chronic psychotics, all of whom manifested some gross disturbance of behaviour. This paper describes the experimental method which was used; the results which were obtained; and a general comment upon the possible implications of the results in relation to other drugs used in psychiatry.