The drug difference between a low and a high dosage of haloperidol was investigated in 40 acutely ill schizophrenic patients. All patients were classified as being thought disordered or non-thought disordered schizophrenic using psychometric methods. From the pool of 40 patients two groups were randomly chosen for the double-blind study, one group receiving 80 mg of liquid haloperidol daily, the other group 16 mg of liquid haloperidol daily. On 5 days during the 21-day treatment the psychopathological state of the patient was evaluated by means of the AMDP system.