CHICAGO—Following a party celebrating her 26th birthday Saturday, a disappointed Kristin Thennes reported that her friends from work failed to mingle with her other friends.

Three of Thennes' coworkers keep to themselves.

"I was really hoping that my work friends would hit it off with everybody else," said Thennes, a budget administrator at Loyola University Medical School. "But the six of them just sort of kept to themselves the whole night. I felt like a terrible host."

The six coworkers invited to the party arrived in a group at approximately 8:45 p.m. Rather than socialize with the 20 or so guests already present, they huddled together near the front window of the living room of Thennes' Andersonville apartment.

"Maybe I'm being a little paranoid, but Kristin's work friends didn't seem to like us," said Laura Romo, 25, an old college friend and Thennes' former roommate. "I mean, they weren't hostile or anything, but they definitely kept their own little circle the entire time."

The coworkers' precious few interactions with the others were brief and occurred only at moments of forced proximity, such as when getting drinks at the bar or waiting in line for the bathroom. Even during these moments, few words were exchanged, with encounters limited to fleeting eye contact and tense smiles.

"They seemed a little older than everyone else at the party," Romo said. "Or maybe they just seemed that way because they were, like, a little stiff and dressed sort of dorky. Everyone else was all casual in jeans, but the work friends were wearing Dockers and stuff. I'm guessing most of them probably live in the suburbs."

Thennes has worked at Loyola's medical school since 1999. During her time there, she has formed many close ties with coworkers, in spite of their lack of common backgrounds. Thennes' closest work friend is Denise Schukal, 29, who commutes to work from her condominium in the Chicago suburb of Rolling Meadows. Schukal, whose husband Jeff stayed home with their 15-month-old daughter while she attended the party, was among the non-minglers.

"Kristin's friends were all really nice," Schukal said. "I didn't get a chance to meet many of them, but they all seemed cool."

Thennes attempted to get her work friends to interact with the others, but to no avail.

"I tried pairing up people who might hit it off," Thennes said. "Like, I introduced Harold, my work movie-geek friend, to Emily, my college movie-geek friend. But after exchanging a few brief words about how they both really liked Gosford Park, they just sort of retreated to their original spots. I thought they'd have been a sure thing. What more could I have done?"

Traci Kessler, a longtime friend of Thennes' who knew no one else at the party, was unable to infiltrate the work-friends circle.

"I got on great with Jen's old college buds and a bunch of the other people there," said Kessler, who met Thennes in 1995 in a yoga class. "But when I went into the living room to meet all her work friends, they were all just talking about office stuff. After about two minutes of that, I had to go back to the kitchen. I was like, forget it."