Forget Montezuma's Revenge. The real hazards for business travelers lurk not in their gut, but in their head. Working globetrotters log many miles-and rack up even more psychic stress. A study of nearly 11,000 workers at the World Bank revealed that women who made more than two international business trips a year filed twice the number of psychiatric insurance claims as their stationary counterparts; men, three times as many.

Bernhard Liese, M.D., head of health services at the World Bank, notes that international business travelers are faced with sudden changes in climate, food, language and culture. Time zone changes can compound travelers' disorientation by disrupting circadian rhythms and depriving them of sleep. Working hours may be extended to make the most of the trip-and in addition to all this, the traveler experiences separation from home and family.

But Liese says that the worst part of business travel may be the return to the office: phone and e-mail messages, not to mention more work, may have piled up while the traveler was away.

Doesn't the domestic business traveler encounter the same stresses? Not necessarily, Liese believes. There's a lot less psychic dislocation in flying to Kalamazoo than Timbuktu.