Heat gas or charcoal grill. If potatoes are large, cut in half or quarter for uniform pieces. Place potatoes in 8-inch square disposable foil pan or in center of large sheet of heavy-duty foil.
In small bowl, mix butter, garlic and salt; pour over potatoes. Cover pan with foil or seal foil packet with double-fold seals, allowing room for heat expansion.
When grill is heated, place potatoes on gas grill over medium heat or on charcoal grill over medium coals. Cook 35 to 45 minutes or until potatoes are tender, stirring potatoes in foil pan or turning foil packet several times during cooking.