The literature is reviewed, and a case is presented of an acute psychotic reaction following the onset of phenothiazine therapy. The patient also suffered from loss of several sensory reactions and was considered a natural experiment in sensory deprivation. The author has speculated about the relationship between phenothiazine-induced toxic psychoses and sensory deprivation. The possibility is raised that phenothiazine drugs rather than having directly toxic effects on brain substance could produce acute brain syndromes through secondary effects on sensory input and perhaps through alteration of anxiety and agitation.Abstract Teaser