Dopaminergic oversupply relative to intrinsic striatal cell loss is thought to underlie the involuntary movements of Huntington's disease (HD). Tetrabenazine (TBZ) and haloperidol, two antidopaminergic compounds differing in their mechanism of action on the nigrostriatal pathway were compared in 11 HD patients in their ability to decrease the choreatic movements in a single-blind cross-over study. Though improvement in chorea scores over baseline values was greater under TBZ (46.3 +/- 23.4) than haloperidol (28.6 +/- 47.7), the difference did not reach statistical significance (Student t tests). All 11 patients improved to some extent during the TBZ phase, and in 6 it was greater than while under haloperidol. However, haloperidol reduction in the chorea scores was significantly greater in 3 patients, while there was no difference in 2 other cases. Severe depression occurred in 3 patients under TBZ, in one leading to attempting suicide, while tardive dyskinesia complicated haloperidol therapy in 3 patients. The later drug could be an alternative therapy for those patients in whom TBZ provides unsatisfactory control of the choreatic movements, but it might be the drug of choice in cases with associated depressive illness or organic psychosis.