Heat oven to 350 degrees. Beat butter (or margarine) until creamy. Add the 2 sugars, and beat until well blended. Add the eggs, and beat until smooth and light; then add the peanut butter, and mix well. Combine the flour, baking soda and salt. Add to the peanut butter mixture, and beat well. Roll dough into small balls, and place on ungreased cookie sheets. Press each cookie with the back of a fork (in a criss-cross design) dipped in flour, if it sticks to dough. Bake 8 to 10 minutes, or until edges are SLIGHTLY brown. Remove from sheet to cool and crisp, before storing. Makes about 120 cookies. (I make mine twice as big...and usually get about 60 cookies.) NOTE: These cookies freeze well. ----