In a nonporous glass dish or bowl, combine the mushrooms, vinegar, rosemary, and salt and pepper. Stir to coat. Cover, and refrigerate for at least 30 minutes.
Preheat grill for high heat.
Brush grate with oil, and arrange marinated mushrooms on hot grill. Turn after 2 to 3 minutes, and continue grilling until mushrooms are heated through and look wilted and black. Serve hot off the grill.
