ST. MARY’S CITY, Md. — Rachel Brill and Mary McCarthy are seniors and longtime roommates at St. Mary’s College of Maryland. This year, they share their four-bedroom campus apartment with two other female students. Also, Theo and Carl.

Theo, easygoing and unflappable, is a tawny, 103-pound, longhaired German shepherd. Carl, an energetic charm magnet, is a jet-black, 1.5-pound Netherland Dwarf rabbit.

House rules: Carl must reside in a pen under Ms. McCarthy’s raised bed; Theo snoozes in a crate in Ms. Brill’s bedroom. Carl cannot be let loose in the living room, where Theo likes to hang out. “We’re still very careful because we don’t want there to be an issue with Theo and Carl,” Ms. McCarthy said. “We’re both very anxious people.”

And that is exactly why Theo and Carl have permission to live in campus housing.

Like many schools across the country, St. Mary’s, a small, public liberal arts college, is figuring out how to field increasing requests for animals by students with diagnosed mental health problems. Last fall it began allowing “comfort animals” for students like Ms. Brill, Theo’s owner, who has anxiety and depression, and Ms. McCarthy, Carl’s owner, who gets panic attacks.