This collaborative study on the efficacy of high doses of trifluoperazine in chronic schizophrenia showed that treatment response was related to length of hospitalization; short-term patients benefited most. High doses of trifluoperazine were most effective with those short-term patients who had been on a piperazine phenothiazine prior to the study. Also, most placebo patients who had been receiving low doses of phenothiazines before the study did not suffer deleterious effects while they were off medication. Treatment implications are discussed.Abstract Teaser