In a double-blind, crossover study gamma-vinyl GABA, 2 g/day, and placebo were administered orally for 2 weeks each to six patients with Huntington's disease. Five patients were treated concomitantly with a neuroleptic maintained at constant dose. No consistent beneficial effects on the hyperkinetic movements, abnormal motor function, or ability to carry out normal activities were evident with gamma-vinyl GABA treatment. Treatment was tolerated without clinically significant alterations in the physiologic or biochemical tests used for monitoring. These results suggest that increasing CNS GABAergic function is unlikely to ameliorate Huntington's disease.