We prospectively studied 244 consecutive patients with subarachnoid hemorrhage who were admitted within 72 hours to the same institution between November 1977 and May 1987 and who were not treated with antifibrinolytics. From November 1977 through December 1982 (the first study period), daily fluid intake was 1.5-2.1 and fluid restriction was applied when hyponatremia developed; antihypertensives were administered to all patients with high blood pressure. From January 1983 through April 1987 (the second study period), daily fluid intake was at least 3 l, fluid restriction was not applied, and antihypertensives were administered only when patients were receiving this treatment before admission; calcium antagonists were not administered. Entry variables of the patients admitted during the two study periods were not significantly different, although patients admitted during the second study period were at slightly increased risks of developing cerebral ischemia and of having a poor outcome. Despite this, cerebral ischemia occurred less frequently among patients admitted during the second study period than among those admitted during the first (16 [10%] of 155 patients vs. 19 [21%] of 89 patients; p = 0.030). Overall mortality decreased from 46% to 36% while mortality among patients with cerebral ischemia decreased from 60% to 31% (difference not significant). Rebleeding and acute hydrocephalus occurred with the same frequency among patients admitted during both study periods. We conclude that the combination of increased fluid intake and the avoidance of antihypertensives helps prevent cerebral ischemia after subarachnoid hemorrhage.