Eleven of 31 clinical centers participating in the Italian Acute Stroke Study--Hemodilution carried out a preliminary study on the effectiveness of ganglioside GM1 in acute stroke; 502 patients were randomized to GM1 (GM1, n = 121), GM1 plus hemodilution (GM1 + H, n = 128), placebo (P, n = 130), or placebo plus hemodilution (P + H, n = 123) groups less than or equal to 12 hours after onset of a hemispheric cerebral infarct. The patients were treated for 15 days and were evaluated on Days 21 and 120 after the onset of stroke. Intention-to-treat analysis failed to show any differences in neurologic deficit, mortality, or neurologic disability among the groups. Efficacy analysis showed a significantly higher degree of neurologic improvement in GM1 group patients compared with patients in the P group during the first 15 days. GM1-treated patients (GM1 and GM1 + H groups) showed a significantly higher degree of neurologic improvement during the first 10 days compared with the placebo-treated patients (P and P + H groups). These differences were no longer statistically significant at Day 120. Our results provide a rationale for the planning of a larger, multicenter trial of GM1 ganglioside in acute stroke.