WWW- John Schulz, Marriott International’s director of quality control, had something to discuss last November at one of the hotel industry’s biggest conventions — something that really makes people squirm.

At the International Hotel/Motel and Restaurant trade show in New York, Mr. Schulz spoke at a symposium called “Stop the Spread of Bedbugs.” The pamphlet advertising the event, printed by pest-control company Ecolab, promised a discussion of “the reasons behind the resurgence of these unwelcome pests.”

Mr. Schulz declined to comment on his presentation, and Marriott said it doesn’t have a bedbug problem. But people in the hotel industry are waking up to the fact that they are playing host to some particularly nasty guests. In the past few years, Cimex lectularius — the common bedbug — has been making a small but alarming comeback, in part because some of the pesticides that had kept them at bay have been phased out.

Hotels are particularly vulnerable to infestations because the bugs travel in luggage and clothing and because hotels have so many different people sleeping in their beds.

A survey of insect-control companies in 2004 by Pest Control Technology magazine found that hotels accounted for the biggest proportion of all reported bedbug infestations. Respondents said 37% of bedbug calls came from hotels and motels. That was up from 31% the year before. Orkin Inc., the pest-control company, reports a substantial increase in its bedbug calls in the past year.

Bedbugs nest on or near mattresses and feed at night by biting and sucking the blood of people as they sleep. They can cause itchy red welts and considerable, lingering anxiety. They’re nearly impossible to get rid of without treating bedding and furniture with powerful pesticides. (Throwing everything away works, too.) The good news is that bedbugs are not known to transmit diseases.

The comeback of the bedbug is turning into a legal and public-relations headache for the hotel industry. In recent weeks, a Florida couple said they were bitten by bedbugs on a Royal Caribbean International cruise ship off Fort Lauderdale, Fla., according to their lawyer, Terry M. Rosenblum.

Royal Caribbean says it refunded them $2,800 for their cruise, paid for hotels in Puerto Rico, and flew the couple back home. In a statement, the company says, “Our laundry process cleans all bedding at 155 degrees, a recognized practice that prevents such occurrences as ‘bedbugs.’ ” The company says that “in this case, it appears that the bugs were brought onboard by a previous guest and were found in areas other than the bed.” It says the bugs have been eradicated.

Still, some travelers are worried. “We’ve had 20 to 25 calls a day” from concerned customers, says Jai George of cruisenetwork.com, a Raleigh, N.C., cruise specialist.

Charles Kelley, a physician and an executive at Outrigger Enterprises, Inc., which owns or manages 46 hotels in Hawaii, the South Pacific and Australia, is one of the rare hoteliers willing to discuss the bedbug issue openly. He keeps a jar of dead bedbugs on a shelf in his office. He uses it to train staff about what the critters look like. He says companies can avert lawsuits by being forthright with guests. But, he says, “No hotel chain wants to talk about this.”

Last month, a family of three filed suit against a Days Inn in Ottawa. Their suit, in the Ontario Superior Court of Justice, alleges that in July 2003, they awoke at 5:30 a.m. to find dozens of bedbugs walking on the sheets. Since then, they have been “unable to participate in recreational and social activities to the extent to which they participated in such activities prior to the incident,” according to the complaint. They have also incurred fumigation and other expenses, it says.

David Young, a lawyer for the hotel, says the hotel had no previous complaints. He says he can’t comment further while his investigation is continuing.

In February, two North Carolina women filed suit in Durham County Superior Court against Days Inn and one of its franchisees for renting them an infested room a year earlier in Durham, N.C. When the pair went to the front desk to complain, the suit alleges, the clerk “became very agitated, picked up a pen, pointed the pen at them in a threatening fashion and told them to either take another room or get out.” They are asking for damages of more than $10,000 each, plus expenses.

A lawyer for the firm representing the franchisee, C. Scott Holmes, says he can’t comment at this early stage. Days Inn, a unit of Cendant Corp., declined to comment.

Some people say the bedbug claims are being blown out of proportion, partly by unscrupulous litigants. Thomas Jones, an associate professor at the University of Nevada Las Vegas’s hotel school, says bedbug claims are among the top frauds perpetrated against hotels.

As recently as the early 20th century, the tools to fight bedbugs were crude but effective. One anti-bedbug guide from the 1920s advises treating infested mattresses with “high-test gasoline.” A 1935 guide prescribed powdered calcium cyanide.

Bedbugs truly met their match when DDT became a household item in the late 1940s. But DDT was banned in 1972. The Environmental Protection Agency phased out two organophosphates that were favorite bedbug killers in recent years, because of their potential danger to humans. And a lot of people, these days, are uncomfortable with using pesticides at all, particularly in the beds they sleep in.

The EPA says that 673 pesticides are registered and still available to treat bedbugs. But Michael Potter, an entomologist at the University of Kentucky, says they’re less effective than pesticides of old.

Dr. Potter, who maintains a collection of historical material about bedbugs, says one of the first references to the critters in literature was in “The Clouds,” by Aristophanes in 423 B.C.

When Socrates tells Strepsiades to move a couch into the room, Strepsiades responds: “But the bugs will not allow me to bring it.” At one point, Strepsiades says the bugs are poking him in the posterior.

Their resurgence today startles even bug experts. Gary Bennett, a professor of urban entomology at Purdue University, has studied insects for 50 years and says he hadn’t seen a case of bedbugs until recently. He didn’t think they existed in significant numbers but became a believer last year when one of his students was bitten in a hotel in Salt Lake City. “You know infestations are on the rise when someone in the entomology department gets bedbugs,” Dr. Bennett says.