Heat oven to 250 degreesF. Spray roasting pan with no-stick cooking spray. Place cereal in prepared pan.
Combine brown sugar, butter and syrup in 3-quart saucepan. Cook over medium-heat heat until mixture comes to a boil (8 to 9 minutes). Continue cooking, stirring constantly, 1 minute. Remove from heat. Add baking soda; mix well.
Pour syrup mixture over cereal; toss gently until well coated. Bake for 40 to 50 minutes, stirring every 15 minutes, or until coating is set.
Spread mixture onto waxed paper. Cool 10 minutes. Break apart. Store in container with tight fitting lid.