PHENOTHIAZINE tranquillizers inhibit conditioned responses of various laboratory animals. Since this action can be demonstrated by means of a great variety of methods, it is generally considered to be characteristic of these compounds. Some tranquillizers also diminish ‘emotional reactions’1–4; but these effects have not been studied so much, mainly due to a lack of simple and adequate methods. Thus, views are still divided whether depression of the emotional reaction is a primary effect or an effect secondary to the sedative action of such drugs3,4. Any new technical procedure which permits the study of the influence of a drug on emotional behaviour independent of its general depressive effect, therefore, appears interesting.