This is a multicenter randomized double-blind placebo controlled parallel group study evaluating the efficacy and safety of GV150526 or placebo in patients with a clinical diagnosis of acute stroke. This drug is a potent glycine antagonist. Glycine is a co-agonist of the n-methylanine d aspartate (NMDA) receptor for glutamine-induced and neuroexcitation. Since overstimulation of this NMDA receptor by glutamate may be cytotoxic during cerebral ischemia, antagonism of this receptor may be beneficial. This study is designed to evaluate the efficacy of the drug at 3 months when given within 6 hours of acute ischemic attack and confirmed hemorrhagic stroke.