A recent study showed an adjuvant effect of carbamazepine in the neuroleptic treatment of acute schizophrenic psychoses. Since beclamide (beta-chlorpropionamide) was reported to reduce the neuroleptic doses required, the combination haloperidol-beclamide was tested using a double-blind, placebo-controlled study in 23 inpatients with an acute schizophrenic psychosis. In both groups patients received haloperidol and either beclamide or placebo. Every 7 d the treating psychiatrist could increase the haloperidol dose by 3 mg per day if clinically necessary. Chlorprothixene and biperiden were on hand as additional medication. After 28 d beclamide or placebo were discontinued under a constant dose of haloperidol and a final rating with the Inpatient Multidimensional Rating Scale, Brief Psychiatric Rating Scale, and Extrapyramidal Symptom Scale was carried out. Without reaching statistical significance, the beclamide group needed a lower dose of neuroleptic medication, showed fewer side effects and a more pronounced psychopathological improvement.