Joseph Marschhauser and Norman Ringle have been dear friends for decades. They attended library school together and today both work as librarians at New Utrecht HS in Bensonhurst. They share a love of food, travel and books. Now they have one more thing in common.

“I gave a kidney to Norman,” Marschhauser, 57, says matter-of-factly. “He insists it’s a loan and I can have it back whenever I want.”

Humor is a cornerstone of their friendship, but the laughs have been coming with more frequency since Sept. 22, when Marschhauser donated one of his kidneys to Ringle, 58. If not for the transplant, Ringle, who was in late-stage renal failure, would have had to endure dialysis for the rest of his life.

“I read that people who donate a kidney live longer so I donated one of mine,” Marschhauser quips, before turning serious. “Norman had diabetes and his health was getting worse. He was out a lot. Unsteady on his feet.”

Marschhauser said the decision wasn’t so difficult to make.

“People tell me it’s a big deal,” he said. “Morally, it’s the right thing to do. Besides, it makes me happy to help Norman.”

Ringle was returning from arranging the funeral of his beloved mother last summer when Marschhauser told him that he’d gotten tested and their blood types matched. The transplant was a go.

“He was resolute as a human being and a friend,” says Ringle. “I would have done the same for him, but I have to say that the decision would not have been as easy for me.”

Marschhauser has already returned to the stacks, but Ringle won’t join his fellow librarian for a month or two. Meanwhile, Ringle has been tackling his diabetes — “my current torment” — with vigor.

So far he has lost 50 pounds. “Lovely to be reintroduced to clothing I haven’t been able to wear in years,” he says wryly.

With his improving health, Ringle hopes he and Marschhauser will hit the road this winter for what used to be their annual visit to the Sunshine State and eventually to more far-flung locations, including New Zealand.

But first things first: the celebratory dinner. The restaurant has yet to be chosen. But one thing is settled: “He’s paying,” says Marschhauser. “I’m paying,” says Ringle.