Preparation Combine grapefruit juice, St-Germain, and Campari in a large pitcher. Cover and chill until cold, about 2 hours. Divide grapefruit mixture among glasses and top off with sparkling wine. DO AHEAD: Grapefruit mixture can be made 1 day ahead. Keep chilled.
Preparation Combine grapefruit juice, St-Germain, and Campari in a large pitcher. Cover and chill until cold, about 2 hours. Divide grapefruit mixture among glasses and top off with sparkling wine. DO AHEAD: Grapefruit mixture can be made 1 day ahead. Keep chilled.