To marinate: Pour salad dressing into a large, resealable plastic bag. Add chicken breasts, seal bag and shake to coat. Place in refrigerator for at least 1 hours or overnight (the longer, the more taste the chicken will absorb).
Preheat oven to 350 degrees F.
Remove chicken from bag, discard remaining marinade. Place chicken in a lightly greased 9 x 13 inch baking dish and bake at 350 degrees F for 1 hour; or, until chicken is cooked through and juices run clear.