The relationship between enlargement of the lateral ventricles in the brains of schizophrenic patients and clinical response to neuroleptic treatment, as assessed by the ventricle-brain ratio (VBR) and psychopathology scores, was studied in a sample of 39 patients with schizophrenia or schizoaffective psychosis during a drug-free washout and after 3 1/2 weeks of treatment with either haloperidol or thioridazine. There was a weak, but statistically significant positive relationship between VBR and improvement on BPRS Psychosis factor scores after 3 1/2 weeks of treatment, and a negative correlation between VBR and baseline (washout) scores on the BPRS Anergia factor. Patients with enlarged VBRs, as defined by two criteria, also tended to show a better response to neuroleptics than patients below these criterion values.