Remove skin and fat from kidneys. Cut them lengthwise in half. Run skewers through them lengthwise to prevent their curling as they cook. If they are small, put 2 or 3 halves on each skewer. Brush all surfaces with melted butter.
Heat broiler for 10 minutes. Put kidneys, rounded side down, on broiler. Cook 3 inches from heat for about 5 minutes. Do not turn.