1. In large bowl combine pretzels, cereal, and M&Ms.
2. In large saucepan over low heat melt butter and peanut butter. Add marchmallows. Cook and stir until marshmallows are melted and mixture is smooth.
3. Pour over pretzel mixture, stir to coat.
4. Press into 13x9x2 inch baking pan. Cool to form and cut into squares.