About half a million Americans are living with multiple sclerosis, a serious disease where the body attacks the nervous system.
It's about three times more common in women, but men can also get multiple sclerosis.
Jeffrey Steenberg was diagnosed with multiple sclerosis, and like half the patients, he had memory problems.
Neurologists say there is no treatment to protect patients from memory failure.
Now, a testosterone gel called AndroGel may help.
In a small study, 10 men with multiple sclerosis applied it to their shoulders once a day for a year.
Rhonda Voskuhl, M.D., of the UCLA School of Medicine, says, "What they reported is that they felt better, that they had more energy and less fatigue."
The gel improved their immune systems and all the patients performed better on memory tests.
MRI scans also showed parts of the brain, which normally decline when affected by multiple sclerosis, actually slowed.