Recent investigations suggest that increased cellular calcium concentrations may be implicated in neuronal death after ischemia. To determine whether treatment with a calcium-channel blocker would improve survival and neurologic outcome in acute ischemic stroke, we enrolled 186 patients in a prospective, double-blind, randomized, placebo-controlled trial of nimodipine (30 mg every six hours), begun within 24 hours of the onset of symptoms of an acute ischemic stroke. During the four-week treatment period, mortality from all causes was significantly reduced with nimodipine as compared with placebo (8 deaths [8.6 percent] vs. 19 [20.4 percent]). The improvement in survival was restricted to men. During the follow-up period of six months, an additional eight patients in each group died. A significantly better neurologic outcome, as assessed by the Mathew scale of neurologic deficit, was also observed in the nimodipine group. The improvement in neurologic status was greatest in patients with a moderate to severe deficit at base line. There were no important side effects except for one episode of reversible azotemia that may have been related to treatment with nimodipine. Our data suggest that patients with acute ischemic stroke may benefit from early treatment with nimodipine, but this therapeutic effect appears to be limited to men.