Preheat oven to 350°. Beat together margarine, peanut butter and sugars until light and fluffy. Blend in eggs. Measure flour and lightly stir in soda. Add combined flour mixture to creamed mixture. Stir in M & M's. Drop dough by tablespoons onto ungreased cookie sheets. Bake for 14 to 15 minutes, or until edges are golden brown. Loosen cookies immediately after removing from oven. Let cool on sheets for 1 minute and place on wire rack to finish cooling. Yield: 3 dozen.