In a large glass dish, mix together the creamy salad dressing, Italian-style salad dressing and cayenne pepper. Add chicken breasts and toss to coat. Cover and refrigerate. Marinate for 1 to 2 hours.
Preheat an outdoor grill for high heat, and lightly oil grate.
Remove chicken breasts from marinade, and grill for 6 to 8 minutes each side, until no longer pink and juices run clear.