Thioproperazine is a phenothiazine compound with a piperazine nucleus in the side chain. The pharmacological investigations of Courvoisier et al. (1958) indicate that it is much less sedative than other phenothiazines and that it has weak anti-adrenaline, anti-histamine and anti-serotonin activity. Clinical reports by Delay et al. (1958), Perrin et al. (1958), Denber et al. (1959), Levy and Maarek (1960) and Perret et al. (1961) indicate improvement in schizophrenic patients, but their papers described trials of this drug in which both recent and long-term cases or other diagnostic groups were included. Denham and Carrick (1961) reported the total remission of symptoms in 32 of 58 chronic schizophrenics treated by the discontinuous method with significant improvement in a further 25. Their acceptance of the view that improvement was correlated with the occurrence of hypertonic syndromes and that failure of treatment was likely if anti-parkinsonism drugs were used to suppress the hypertonicity, excludes the possibility of the type of continuous treatment employed with other phenothiazines. Denber et al., however, advocated the suppression of these drug effects and Perret et al. reported 47% improvement using the continuous method in another mixed group of chronic patients.