The safety and tolerability of single escalating doses of lubeluzole were evaluated in healthy male volunteers in 2 studies. In the first of 2 randomized, single-blind, placebo-controlled, dose-escalation studies, 6 subjects received single 30-minute infusions of 2.5, 5, and 10 mg of lubeluzole, and 2 additional subjects received placebo. In the second study 6 different subjects received a 1-hour infusion of 15 mg of lubeluzole, 5 of whom received the 20-mg dose, and 2 received 25 mg of lubeluzole. Two additional subjects received placebo. Small increases and decreases in PQ, QRS, QT, QTc, and QTm intervals were noted after infusion of all lubeluzole doses and placebo, however, these changes were within the normal ranges for these values except for the QTc for the 25-mg dose of lubeluzole. Significant prolongation of the QTc interval was observed at the end of the 1-hour infusion in both subjects receiving the 25-mg dose of lubeluzole. No clinically relevant changes in systolic time intervals, heart rate, blood pressure, and clinical laboratory values were noted in subjects receiving 2.5-25 mg of lubeluzole or placebo. Adverse experiences, predominantly lightheadedness and dizziness, were reported by subjects receiving doses of lubeluzole greater than or equal to 10 mg. Lubeluzole, administered as single intravenous doses of 2.5-15 mg, is safe and well tolerated in healthy male volunteers.