Washington ? The world of male contraception has been limited to condoms and vasectomies. But researchers now point to a new method that shows promise — a shot that prompts an immune reaction to a protein produced in the male reproductive system.

The method worked in experiments on male monkeys, most of which regained their fertility when the treatments stopped, researchers report in Thursday’s issue of the journal Science.

“Immunocontraception for males is a possibility and hopefully will be developed for human use over the next several years,” said Dr. Michael O’Rand of the University of North Carolina.

O’Rand, lead researcher in the project, said progress depended on funding for the work and that even with unlimited money, translating the findings into human use could take a decade.

In recent years, researchers have developed some male contraceptives, based on hormones, that were designed to suppress sperm production. This work is now in trials.

In O’Rand’s experiments, which did not involve hormones, monkeys were immunized using a form of eppin. That is a protein produced in the testis and epididymis, the tightly coiled ducts that carry sperm.

Male monkeys that developed a immune response to the eppin still were able to copulate but could not impregnate females, the researchers said.

“We don’t understand the exact mechanism yet, but we think the immunocontraception works by preventing the sperm from freeing itself from the seminal fluid to make its way to the uterus and oviducts to fertilize the egg,” O’Rand said.