The hypothesis that schizophrenia is caused by the release of prostaglandin E into the hypothalamus and may sometimes be accompanied by an elevation of temperature was examined by a clinical trial of the prostaglandin E suppressant N-acetyl-p-amino-phenol (paracetamol, acetaminophen). Ten acute schizophrenic patients were included in a double-blind, crossover trial of paracetamol and a placebo, in which each treatment was given for a week. Regular 4-hourly temperatures were recorded in all these cases and in 5 non-schizophrenic patients for comparison. The findings provided no evidence that paracetamol mitigated the symptoms of schizophrenia. The temperatures of the schizophrenics were not elevated more than those of the controls, but the number of cases used was probably too small for this finding to be conclusive.