Anyone interested must first register at www.flexpetz.com before meeting Mr. Haddix. “I ask them a lot of questions,” he said. “I want to know if they have ever owned a dog, why they can’t own a dog full time, how renting a dog benefits them, stuff like that.”

If the head office in San Diego gives the go-ahead, there is a mandatory one-hour training session on handling and training. Then members can choose one of the dogs pictured on the Web site for rental.

Mr. Haddix said his customers were a mixed bunch.

“There are people from other states and other countries who couldn’t take their dogs with them when they were transplanted to New York,” he said, “and there are families with small children who enjoy taking these dogs on vacation with them.

“There are also people who live in places that do not allow pets, and a lot of single people who wouldn’t mind just hanging out with a pal every now and then. There are all sorts of reasons for renting dogs,” said Mr. Haddix, who is studying for a master’s degree in philosophy at the New School for Social Research when he is not studying the qualifications of prospective renters.

Mr. Haddix noted that big dogs are rented out on the West Coast, where the dogs generally have more room to roam, and smaller dogs are rented in New York, where, as he put it, “many people live in apartments the size of coat closets.”

Stacy Faulkner, 39, is a Flexpetz client in San Diego. She has been married for 10 years and does not have children, she said, so “renting a dog can really fill a void.”

Two years ago, her 10 ½-year-old Rottweiler, Kaya, died.

“When you don’t have kids,” Mrs. Faulkner explained, “your animals are like your own children, or a new best friend.”