Ozie Lewis took a deep breath and looked up as he returned to work on the 83rd floor of Chicago's Sears Tower, the nation's tallest building.
"That's way up there, so you can't help but be nervous," said Lewis, who works for an insurance company. "I just hugged my wife and my son a little bit tighter this morning."
Shaken by Tuesday's terrorist attacks in New York and Washington, people who work in the towering landmarks that form the skylines of the nation's cities have been nervously scanning the clouds for planes, avoiding elevators and jumping at the sound of sirens.
At many skyscrapers around the country, security has been tight, with guards carefully screening workers' identification. New York's Empire State Building, closed to tourists, has opened to workers, but its halls and elevators were much less crowded than usual late last week.
Anna Borys, an architect, showed up for work on the 12th floor, though she said she feels the Empire State Building is "the No. 1 target now."
"I like my work, and I will come to work," Borys said. She found the incessant sirens oddly reassuring. "That's proof that everything will be fine," she said.
Andrea Mendez, a lawyer on the 44th floor, also went to work Friday but was feeling numb. "I am evaluating everything, including living in New York City," she said.
Across the country, William Boyd, a concierge at the Columbia Tower Club in the tallest building in Seattle, peered from his window on the 75th floor and said he will never feel the same about watching the heavy air traffic from nearby Boeing Field.
"I used to like watching those planes. Now I'm just watching them all very closely," he said. "I'm certainly anxious about being here, but in all honesty I believe I'm safe."
Several of Boyd's colleagues and customers weren't as confident. By Thursday, two employees, noting security issues, had quit, and all banquets scheduled for the week had been canceled.
Skyscrapers traditionally have been symbols of the economic might of the United States, said architect Robert Ivy, editor of Architectural Record magazine.
In the future, "People may choose not to have a building that sets itself apart as obviously," he said. "This is not the end of the skyscraper, but we may avoid iconic buildings, buildings that stand out."
At San Francisco's Transamerica Building, workers anxiously watched the sky for airplanes.
"Wednesday was really tough to be in the office," said consultant Rory Keogh.
A few blocks away at the Embarcadero Center, legal secretary Tina Richardson said her perch on the 34th floor made her feel vulnerable. When a bomb threat came in, Richardson took the stairs instead of an elevator. It took her 10 minutes to get out.
"The whole way down, I kept thinking, what would happen if an airplane hit while I was in the stairwell?" she said. "It was frightening."
In Los Angeles, a false fire alarm Wednesday rattled nerves at the 52-story Bank of America building. But Cheryl Garland, 43, who works in the black stone tower as an executive secretary, said she wouldn't let the terror attacks shake her.
"It's more important to us to demonstrate that the act of terrorism will not stop us," she said.
At the Sears Tower, Jim Damico said, "Thirty years ago, I served in the Marines, and we didn't let anyone push us around. Be damned if I'm going to let them do it now."