In large roasting pan, combine cereal and peanuts; set aside.
In medium saucepan over medium heat, combine sugar, butter, syrup and peanut butter. Bring to a boil, stirring constantly; boil 1 minute, stirring constantly. Remove from heat.
Stir in vanilla and baking soda (mixture will foam). Pour over cereal mixture; toss to coat.
Bake in a preheated 250°F oven 30 minutes, stirring every 10 minutes. Remove from oven and spread on wax paper to cool. Store in an airtight container.