Thirty-two schizophrenic patients, previously treated with antipsychotics, were treated with haloperidol decanoate and flupenthixol decanoate in a double-blind cross-over study. The drugs were given for 24 weeks each at an individually adapted dose. The last three injections of either drug were given at fixed 4-week intervals. The mean dose over the two treatment periods changed from 131 mg (start) to 151 mg (week 24) in the haloperidol decanoate group and from 56 mg to 66 mg in the flupenthixol decanoate group, the inter-drug ratio being 2.3:1. During the first study period, the patients' condition remained rather stable with both drugs. After crossing-over, the symptoms were further reduced with haloperidol decanoate but increased with flupenthixol decanoate. Side effects of the two drugs were comparable and were generally few and mild. It was concluded that 4-week intramuscular administration of haloperidol decanoate provides appropriate control of schizophrenic symptoms, but that flupenthixol decanoate should be dosed at shorter intervals.