AB - The therapeutic and unwanted effects of the new long-acting antipsychotic, haloperidol decanoate, were evaluated in 32 stabilized chronic schizophrenics, in a double-blind, randomized, placebo-controlled trial. The follow-up period was 16 weeks and the medication was injected intramuscularly every four weeks. The starting dose was ml (equivalent to 150 mg haloperidol) and subsequently was titrated according to the therapeutic and unwanted effects. Deteriorated patients were treated temporarily with active haloperidol tablets. Patients needing more than 3 ml of the . medication or more than 40 mg haloperidol tablets daily, were excluded as failures. Out of the 16 patients included in the active drug group, 11 remained under control, 5 were even improved, very few needed treatment with active haloperidol tablets and none was evaluated as therapeutic failure/ the BPRS and the NOSIE-30 were significantly improved in the haloperidol decanoate group. Patients in the placebo group mostly deteriorated, 13/16 needed additional treatment with active haloperidol tablets and 13/16 were evaluated as therapeutic failures. Less antiparkinson treatment was needed in all patients compared o the pretrial period.