Preheat the oven to 190 degrees C. Grease baking trays.
In a medium bowl, cream together the margarine, white sugar and brown sugar until smooth. Beat in the eggs one at a time then stir in the vanilla. Sift in the flour, bicarb soda, salt and cocoa powder; mix well. Stir in the chocolate chips. Roll tablespoonfuls of dough into balls and place them 3cm apart onto the prepared baking trays.
Bake for 8 to 10 minutes in the preheated oven. Allow biscuits to cool on baking tray for 2 minutes before removing to a wire rack to cool completely.