Preheat oven to 375 degrees F (190 degrees C). Grease and flour a 9x13 inch pan.
In a large bowl mix together flour, sugar, cocoa, baking soda and salt. Make a well in the center and pour in the water, vanilla and mayonnaise. Mix well, then stir in the chocolate chips.
Pour batter into prepared pan. Bake in the preheated oven for 40 to 50 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.
