The postulated deficiency of prostaglandin E1 series (PGE1) in schizophrenia has been investigated in a controlled therapeutic trial. Twenty-one inpatients with a schizophrenic illness resistant to neuroleptic drug treatments were randomly assigned to one of three treatment conditions in a blind controlled trial of dihomo-gammalinolenic acid (DHLA), a PGE1 precursor. Patients received depot neuroleptic medication and DHLA capsules, placebo depot medication and DHLA capsules, or placebo depot medication and placebo capsules. No marked treatment effects were noticed on ratings of the patients' behaviour or symptomatology, though some clinical effects were noted in dyskinetic patients. Abnormalities in red blood cell lipids were observed in the patients entering the trial, suggesting that further investigation of an EFA/prostaglandin deficiency hypothesis in schizophrenia is worth pursuing.