Lightly grease a 9 x 13 baking dish or pan. Set aside.
Place cake mix, beaten eggs, oil and water in a mixing bowl. Beat on medium till all is moist. Beat on high for another minute or two.
Fold in the chocolate chips and marshmallows.
Spread evenly into the prepared baking pan.
2Bake for 20 - 25 minutes. It's hard to check this cake for doneness, due to the chips and marshmallow...I try to find a spot in the center of just cake and test with a pick...it's usually done between 20 - 25 minutes.