The therapeutic efficacy of GABA was compared with pyrithioxine and placebo in 432 patients with cerebrovascular disorders by a multi-center (50 hospitals) double-blind clinical trial. 12 tablets (3 g) of GABA and 3 tablets (600 mg) of pyrithioxine were given daily for 8 weeks. Subjective complaints, neurological and psychiatric findings, activity of daily living were checked at the 4th and 8th weeks after medication. The global improvement rates in GABA-treated groups were 59% and 70% each after 4 and 8 weeks of medication, and were significantly superior to the other two groups. Especially on cerebral arteriosclerosis GABA was more effective than the other two drugs, with statistical significance. As for improvement rates of symptoms there were significant differences between GABA and the other two drugs in subjective complaints and in psychiatric findings. The incidence of side effects was 5%, 20% and 8% in GABA, pyrithioxine and placebo, respectively. The incidence of abnormal laboratory data was 2% (3 cases), 8% (11 cases) and 4% (6 cases), respectively. Those in GABA group were transient and restored to normal values after the trial. It is concluded from these results that GABA is safe and effective in the treatment of cerebrovascular disorders.