A: n most cases, absolutely nothing, according to Yvonne Haynes, spa director at the Ritz-Carlton, Key Biscayne. Therapists generally prefer to direct their attention to your stiff shoulders instead of futzing with your underthings. But you won't be wandering the halls in the buff. Upon arrival, you'll receive a robe and slippers to wear and a locker for stashing clothes. Don't be tense about shucking off your thong—employees are as used to the human body as doctors are. (If you must keep your knickers on, request disposable undies to save yours from lotion stains.) On the table, you'll be draped so only a little epidermis is exposed at a time—which means you'll never have to flash more of your bod than you would on the beach. Exceptions to the naked rule: For water treatments like Watsu, clients usually don bathing suits, while loose clothing should be worn during stretching-intensive sessions of Shiatsu and Thai massage. When in doubt, ask for clothing guidelines.