Steve Owens had always left birth control to his wife, who took the pill. After all, male methods were vasectomy, which he did not want, and condoms, which he described as: “Well, condoms are condoms.”

Then Mr. Owens volunteered to test potential methods that lowered his sperm count so much that “I was not viably able to produce a child,” he said. His count rebounded weeks after stopping each method, and he fathered a daughter between research studies.

“I would definitely do some kind of long-term male contraceptive,” said Mr. Owens, a 39-year-old school social worker from Seattle.

Male contraceptives are attracting growing interest from scientists, who believe they hold promise for being safe, effective and, also important, reversible.