Dennis Holden visited Chicago on business recently and had to book a room a half-hour drive from downtown because a radiologist convention filled the central hotels. The city considers his inconvenience a major victory.

Chicago's tourism bureau is wringing concessions from labor unions and expanding meeting space to prevent more of the $56 billion in annual U.S. convention spending from slipping to Las Vegas and Orlando. "We couldn't catch a taxi because of this convention," said Holden, 58, a spokesman for the Commodity Futures Trading Commission.

The five biggest conventions in Chicago, including the meeting of the Radiological Society of North America, the world's largest medical gathering, are adding about $700 million to the city's economy. Chicago needs the revenue: Mayor Richard M. Daley eliminated 320 vacant city jobs and raised taxes on retail sales, cigarettes and alcohol to close a $220 million deficit in this year's $5.1 billion budget.

Chicago, home to North America's biggest convention center, the 2.2 million-square-foot McCormick Place, hasn't been the number one U.S. convention city since 1993. The city hosted 18 major trade shows last year, its worst showing in at least 15 years and less than half the 38 for Las Vegas, according to data from Tradeshow Week, a Los Angeles-based journal focusing on the exhibition industry.

Orlando matched Chicago last year in the number two spot in shows for the first time. Both Las Vegas and Orlando have more hotel space than Chicago, with at least 100,000 rooms in each downtown area, according to their tourism bureaus. Chicago has 30,000 downtown hotel rooms.

The city has worked with unionized labor to cut costs, said Bill Utter, the acting chief executive of the Chicago Convention and Tourism Bureau. Until 1997, he says, exhibitors at McCormick Place were delayed in setting up because they had to use separate teams of carpenters and decorators to build booths, jobs typically done by one class of trades workers in other cities.

Concessions won eight years ago, after the radiologists threatened to leave Chicago, ended the two-team practice and helped convince the group to stay through at least 2010, says Steve Drew, an assistant executive director at the Oak Brook, Ill.-based Radiological Society, which has met annually in Chicago since 1985.

In May, McCormick Place reached a labor accord that includes extending regular work hours, a change the complex's general manager, David Causton, says may stem the losses.

The city has scheduled 39 events so far for 2006, the most since 2000. Coverings, a meeting of people who sell tile and stone products, chose Chicago for its 2007 convention after gathering for 18 years in Orlando and other cities, Causton says.

"We want to be as competitive as we can be," Causton said.

Unions say they agreed to maintain work for members.

"Although it was painful for the members, we took the stance that we've got to do what it takes to get the shows to come to Chicago," said Michael Fitzgerald, president of the United Steel Workers of America Decorators Local 17, one of four unions that agreed to labor concessions in May.

The city is expanding McCormick Place with an $850 million hall that will be completed in 2008. About 37 meetings are signed up to use the new space.

Hotel space remains a primary focus. Chicago is adding 3,000 hotel rooms in the next three years, after building 5,000 during the past decade, said Marc Anderson, the tourism bureau's managing director.

Rooms were the topic of a meeting he called in September of the city's hotel managers and directors of sales to discuss luring the convention of the American Academy of Orthopaedic Surgeons. The group, based in the Chicago suburb of Rosemont, has not held an annual meeting locally in decades because of cold winters. It was seeking a venue after Hurricane Katrina ruined its plans for a New Orleans meeting.

Bringing the group to Chicago in 2006 would boost the odds of the organization returning, he says he told the gathering. The managers agreed, reserved half their downtown rooms for conventioneers, and the surgeons selected Chicago as the site of their March meeting.

Mayor Daley's efforts extend beyond hotels. He's hung banners and signs telling convention attendees "We're glad you're here" at the airport, along the city's main shopping streets, in taxi cabs and at restaurants.

Although the mayor may be happy the radiologists are in Chicago, the CFTC's Holden is not as thrilled when he is stuck a half hour from downtown.

"Anything at the McCormick has this effect," he said.

Chicago's McCormick Place, the nation's largest convention center, faces increasing competition to host large events from warmer destinations such as Las Vegas and Orlando.