If your doctor suspects that physical causes are involved, he or she will likely want to take blood tests to check your level of male hormones and for other potential medical problems, such as diabetes. Your doctor may also want to try eliminating or replacing certain prescription drugs you're taking one at a time to see whether any are responsible for erectile dysfunction.

More specialized tests may include:

Ultrasonography. This test can determine the adequacy of arterial circulation in your genital organs. Ultrasonography involves using a wand-like device (transducer) held over the blood vessels that supply the penis. The transducer emits sound waves that pass through body tissues and reflect back, producing an image to let your doctor see if your blood flow is impaired. The test often is done before and after injection of medication to see if there's an improvement in blood flow.
Neurologic evaluation. Your doctor usually assesses possible nerve damage by conducting a physical examination to test for normal touch sensation in your genital area.
Cavernosometry and cavernosography. Cavernosometry is a test that measures penile vascular pressure. Cavernosography involves injecting a dye into your blood vessels to permit your doctor to view any possible abnormalities in blood flow into and out of your penis.
If your doctor suspects that mainly nonphysical causes are to blame, he or she may ask whether you obtain erections during masturbation, with a partner or while you sleep. Most men experience many erections, without remembering them, during sleep. A simple test that involves wrapping a special perforated tape around your penis before going to sleep can confirm whether you have nocturnal erections. If the tape is separated in the morning, your penis was erect at some time during the night. Tests of this type confirm that there is not a physical abnormality causing erectile dysfunction, and that the cause is likely psychological.