Not since the ancient Romans traveled to Bath, England, to soak in that city's healing hot springs have so many vacationers turned to the spa as a remedy for the stresses of modern life.

According to the American Hotel & Motel Association, spa facilities have either recently opened or are currently under construction in hundreds of resorts throughout the United States."Spas are all the rage in hotel and resort development right now, and that trend is being fueled by customer demand," says Marie Bouchard, director of sales for the Radisson Airport Hotel, a teaching hotel for Johnson & Wales University in Providence, R.I.

Victor Lopez, head of Hyatt Resorts, says a spa is now a necessity at resorts. He said spa revenues are up 15 percent to 20 percent, with a significant increase in the number of men visiting spas accounting for much of that growth.

Bouchard says it is the "pampering" aspect of a spa, rather than the prospect of weight loss, that appeals to both leisure and business travelers. In fact, she adds, many meeting planners rank spa facilities as high as golf courses on their lists of "must-haves" when selecting a site for a conference or convention.

Patty Monteson, co-owner of the spa consulting firm Health Fitness Dynamics, agrees. She adds that hotels in northern climates are developing spas as one way to increase business in the off-season. In July, her company completed a spa renovation and expansion at the Newport Islander Doubletree Hotel in Newport, R.I. The new facility is expected to boost the hotel's winter business.

Hyatt is expanding and renovating all of its existing spas in Puerto Rico, Hawaii and Hilton Head, S.C., and is about to open a 20,000-square-foot spa at the Hyatt Regency Beaver Creek, the ski-in, ski-out resort 8 miles west of Vail, Colo., complete with 20 water therapy rooms and other treatment services.

Parrot Cay, a new luxury resort to open in December in the British West Indies, will have a Balinese-style spa offering body treatments of herbs, spices and flowers imported from Asia.

And earlier this year, Manhattan's venerable Barbizon Hotel did away with its full-service restaurant to make room for a $10 million Equinox Spa and Fitness Center. In addition to a spectrum of fitness programs and equipment, the 40,000-square-foot facility features a self-contained spa offering eight different types of massage, a variety of holistic healing arts, and a plethora of beauty regimens.

Caribbean resorts, which traditionally have focused on sun, sand and sea to draw visitors, are finding that spa amenities are good for business. For example, vacation packages at two all-inclusive spa resorts, LaSource in Grenada and LeSport in St. Lucia, include a variety of spa treatments as well as sports, recreation, meals and accommodations.

"Stressed-out baby boomers have discovered what their ancestors knew hundreds, even thousands, of years ago. That spa treatments can rejuvenate and relax your body, mind and soul," Bouchard says. "When you think about it, isn't that what a vacation is supposed to do?"

If you're a first-time spa-goer, how do you decide which treatments are right for you? The Equinox Spa and Fitness Center in New York offers the following list of some of its most popular offerings:

- Body Slimming Cellulite Treatment: Localized massage, followed by a treatment of Sedona mud, essential oils and white algae. Treatment is said to reduce water retention and diminish cellulite and bloating.

- Detoxifying Mud Wrap: Aromatherapy massage, followed by oceanic clay treatment. To cleanse, soften and rehydrate the skin.

- European Facial: A 60-minute cleansing, polishing, therapeutic massage and gentle pore ex-traction.

- Problem-Solving Back Treatment: Deep pore cleansing and exfoliation of the neck and back using a detoxifying sulfur mask.

- La Stone Therapy: Smooth, heated stones are applied to the body as part of a deep penetrating massage to reduce inflammation and release energy.

- Shiatsu Massage: Pressure is applied along the 14 body meridians. Treatment is said to release trapped energy and heal injuries, muscle tension and arthritic pain.

- Sport Massage: Deep strokes are used to stretch, tone and reduce post-exercise soreness (lactic acid buildup) and inflammation. Helps ease the discomfort of injuries.

- Swedish Massage: Combination of light and deep strokes reduces tension, prevents muscle soreness and improves circulation.

- Reflexology: Steady, even pressure is applied to the feet to stimulate healing and clear energy blocks.