Split kidneys and remove fat and connective tissue.
Brush with melted butter (seasoned, if you wish) and place on lightly greased grill 4 to 6 inches above a solid bed of medium glowing coals.
Cook, turning frequently, for 5 to 15 minutes, depending on size.
Kidneys are done when browned on the outside but still juicy and pink on the inside.
Season with salt and pepper to taste.
Slice to serve.