Somebody recently dropped an idea in the suggestion box at Carnegie Mellon University's library that sounded odd, even for a campus known for its punishing workload.

The library ought to buy sleeping bags and allow them to be checked out, the suggestion went. That way, bleary-eyed students need not even leave the building to catch up on sleep.

"I thought to myself, 'Oh Lord,' " remembered Gloriana St. Clair, dean of university libraries.

No, she said, the campus library wasn't about to sanction sleep-outs in its stacks. But it has switched to 24-hour operation during the week while classes are in session, so those who can't get enough Tolstoy or don't want to pull all-nighters alone in their dorm room can hole up in the building until dawn.

Carnegie Mellon joins a growing number of campuses whose libraries are keeping themselves relevant in the laptop age by running at least part of their operation round-the-clock and by making other changes to the services they offer.

Persistent urging from students unhappy with a 3 a.m. closing time persuaded the staff of Hunt Library to experiment in the fall with leaving its basement and first floor open, Dr. St. Clair said. Hunt, like other college libraries, already operated 24 hours during final exams.

The average 20 or so students in the fall who were in the library overnight at any given hour was twice the target, and it was enough to justify making the hours permanent for students who begin the spring semester on Jan. 12.

Some weren't keen on the all-night library, including members of a faculty advisory committee worried about sleep deprivation.

"Students shouldn't be working all night," Dr. St. Clair was told. "They should finish their work ahead of time so they can get proper rest."

Students who pushed the proposal saw it differently.

"We hear you," they told her. "But every now and then some of us have to work all night."

Seated just inside the library's main entrance the final day of exams, Carnegie Mellon junior Rebecca Kim, 20, a chemical engineering major from Norwood, N.J., said she used the overnight hours a dozen or so times in the fall. It wasn't just the computer clusters, which she frequented, but also the faces she saw that kept her motivated.

"It's being surrounded by people who make you realize you're not the only one who's up studying," she said. "When you're home, it's so comfortable. Your bed is right there. You can jump right in. But here, everyone is in the same mode."

Nationwide, the share of campuses boasting all-night libraries is growing, though it's hard without specific data to say by how much, said Erika Linke, president of the Association of College and Research Libraries and associate dean of university libraries at Carnegie Mellon. She cited Villanova University, Penn State University, MIT, the University of Virginia, the University of Illinois and the University of California at Davis, but said there certainly are other campus libraries with at least a study lounge open all night.

It's no doubt a bow to the nocturnal habits of young adults accustomed to 2 a.m. pizza runs or a midnight trip to the fitness center. And it's one more way libraries have kept patrons coming through the turnstiles, even as more and more materials become accessible on line.

Campus library renovation and expansion projects in recent years have incorporated attractive study spaces designed with overnight use in mind, said Jim Rettig, president of the American Library Association and university librarian at the University of Richmond.

His own campus library added overnight hours a while back after hearing frequent requests for late-night access to computer clusters and for a place to escape dormitory noise.

"It's not very busy at all at the beginning of the semester, but it definitely picks up," he said. "There is an uptick around midterms. A lot of people come in studying for their exams."

Group study rooms have gained in popularity with students who increasingly are assigned to complete class projects in teams. In some cases, traditional library rules have been loosened for a generation used to surfing the Web and checking for text messages, even as they scan a hardbound in front of them.

"It used to be that libraries didn't allow food or drinks," Mr. Rettig said. "Most of them do now."

In fact, many have added popular meeting places, shedding their once-sterile library image.

At Carnegie Mellon's Hunt Library, "The Maggie Murph Cafe" is a popular first-floor eatery with a wall display of photos honoring graduates of the former Margaret Morrison women's college at Carnegie Mellon, who were known as the "Maggie Murphs."

The cafe's debut a couple years ago solidified Hunt's standing as a part of the campus social scene and helped reverse earlier declines in usage of some library services, said Dr. St. Clair. A headline in the student newspaper, The Tartan, couldn't resist poking fun at the prospect of a new coffee nook in the middle of a research library.

"Shhh!" it read. "Don't slurp."

But is this latest change, a library open from midday Sunday through 9 p.m. Friday, really such a necessary thing?

Boo Kim, 21, of Ambler, Pa., a Carnegie Mellon student who works on Hunt's circulation desk, initially opposed the idea, convinced the place would get messy at night. But demand is clearly there, he said, noting that on campus "it's rather hard to find a place where you can study with your friends, eat and drink."

Classmate Erin Burnside, 20, doesn't dispute the convenience factor, especially for students unable to find quiet time because roommates with different schedules are watching TV, listening to music or entertaining guests.

Still, she added, glancing up toward a room of students on the homestretch of finals, "I don't know that it's a good thing to be encouraging people to be up until 4 a.m. studying."