The next time you hear your employees grousing about jet lag and the miseries of airline food, you might remind them that frequent flying does have its rewards -- namely, the money they can get for those frequent-flier coupons the airlines give out. Now, moreover, it's easier than ever to trade the coupons for cash.

The bonus programs date back to 1981, when airlines began giving frequent travelers coupons that entitled them to such freebies as first-class upgrades and tickets to the destinations of their choice. Soon, however, dealers began placing classified ads in The Wall Street Journal and other publications offering to convert frequent-flier coupons into cash instead of tickets. Last September, one of the leading market-makers, The Frequent Flyer Ltd., went a step further. The company opened its first storefront in downtown Boston to buy coupons for cash, which it then converts to discounted tickets.

Prices tend to fluctuate according to such factors as airline promotional fares, strike rumors, and concerns about terrorist attacks, explains Tom O'Brien, founder of three-year-old Frequent Flyer. But early last April, the market for most airline coupons was steady. Individuals with 75,000 miles on either American or United, for example, were unloading their coupons for $1,200; 170,000 miles on Eastern fetched $2,000; and 150,000 miles on United (eligible for two first-class seats to China or Australia) was commanding an impressive $2,500.

With bonuses like this, being "on the road" isn't nearly as punishing as it used to be.