Synthetic TRH and PL [prolactin] were administered orally for 3 wk (300 mg/day), to long-term institutionalized chronic schizophrenic patients, within the framework of a double blind placebo controlled crossover study. Significant changes in physiological and laboratory parameters suggested increased thyroid activity, but significant favorable psychiatric and behavioral changes were not observed. This study does not support the idea that oral TRH could be useful treatment for long-term institutionalized chronic schizophrenic patients, who generally respond readily to major neuroleptic drugs.