Our objective was to assess the efficacy and safety of 40 mg/day glatiramer acetate (GA) in patients with ALS. We conducted a double-blind, randomized, placebo-controlled, multicentre trial. Three hundred and sixty-six patients with definite, probable or probable laboratory supported ALS and a slow vital capacity > or = 70% were randomly assigned to treatment with placebo or 40 mg GA daily. The primary intention-to-treat analysis was the comparison between the two treated groups of the rates of deterioration on the ALSFRSR scale. The secondary outcome measure was time to death, tracheostomy or permanent assisted ventilation. Safety and tolerability of GA were evaluated. After 52 weeks of follow-up, the slope of the ALSFRSR score was comparable in the both groups (placebo, -1.00+/-0.06/month; GA, -1.05+/-0.06/month; p=0.48). The secondary endpoint was non-significant with 159 patients (87.4%) alive in the placebo group and 162 patients (88.1%) in the GA group (log rank, p=0.75). The most common events were the injection site reactions (76.1% in the GA group, 14.8% in the placebo group), comparable to the known profile of 20 mg GA. In conclusion, GA at a dose of 40 mg/day did not show any beneficial effect in ALS patients, and safety and tolerability of GA were good in this population.