Fahim had shown that ultrasound applied to the testicles could significantly diminish sperm production in a number of species, including rats, dogs, and monkeys. Its benefits were that it was effective and, apparently, reversible. A few humans (scheduled to undergo testes removal for prostate cancer anyway) even underwent the procedure, and reported only a "gentle feeling of warmth" during application. But because follow-up studies couldn't replicate the findings, interest in the technique waned, and it was largely abandoned by the medical community.

But a recent study in rats may bring renewed hope for the procedure -- and for men willing to undergo it. Commissioned by the Male Contraception Information Project, researchers at the University of North Carolina put to the test the type of ultrasound machine commonly used in medical practices to restore damaged joints. The trick here was that the team, led by James Tsuruta, used the ultrasound to generate damage to healthy testicles.

The researchers applied several variations of the technique, altering the intensity of the ultrasound, the addition of "regular" heat, the distance of the ultrasound from the scrotum, and the number of applications. They found that when ultrasound was applied twice at high frequency, two days apart, for 15-minutes at a time, the success rate was highest. The rats' sperm production was drastically reduced and the sperm that did exist were virtually immotile. The insides of the testes' "seminiferous tubules," which are normally rife with germ cells destined to become sperm cells, were eerily vacant in the treated testes, leaving a large empty space where there would normally be none.

A couple of years ago, another team had shown that a similar procedure was effective in dogs; and newer research, also commissioned by the Male Contraception Information Project, has shown it to work in monkeys, although the application can be awkward (PDF), at least for the humans applying it. "The monkeys didn't seem to mind the treatment a bit, but we were having a rough time of it," said University of California, Davis, researcher Catherine VandeVoort. "Thirty minutes of treatment three times a week is a lot of monkey testicular massage. We felt pretty silly, and it didn't help when the techs would come around and wonder what kind of research we were doing! We were relieved when we finally saw an effect."

One of the major lingering questions is how long-lasting the technique could be, and then, how reversible. The study in dogs showed permanent contraceptive potential, but the study in monkeys found the method to be just temporary. And it's less clear whether the rats in the study mentioned above would be able to procreate after the treatment was stopped, since follow up lasted only two weeks in the rodents (though sperm counts were still low after this period). Exposing the testes to the zap of an ultrasound would probably produce some anxiety in men, unless the safety, longevity, and reversibility of the treatment were extremely well mapped.