Heat grill to medium; oil grates. Place 4 boneless, skinless chicken breasts (about 6 ounces each) in a shallow dish or resealable plastic bag. Add Buttermilk Marinade; turn to coat. Cover; marinate 30 minutes at room temperature -- or up to overnight in the refrigerator -- turning occasionally. (Bring to room temperature before grilling.)
Remove from marinade; season with salt and pepper. Grill until cooked through, 5 to 8 minutes per side.