In small bowl, combine flour, cocoa, baking soda, salt; set aside. In large bowl, beat butter, brown sugar and white sugar until creamy. Add eggs, one at a time, beating well after each addition. Blend in vanilla. Gradually beat in flour mixture. Stir in chocolate chips.

Drop by tablespoonfuls onto ungreased cookie sheets. Bake at 375F for 8-10 minutes. Let stand 2 minutes before removing from sheets. Makes about 3-1/2 dozen.