The differential diagnosis of impotence. The measurement of nocturnal penile tumescence.

The literature on nocturnal penile tumescence (NPT) and impotence is briefly reviewed. Available evidence suggests that measurement of NPT provides objective data, which when combined with a thorough clinical evaluation can be helpful in distinguishing psychogenic from organic impotence in approximately 80% of those patients who present this differential diagnostic problem. Further research is needed to determine whether some psychogenically impotent patients may have impaired NPT. The interdisciplinary evaluation employed at our center is described, and clinical material illustrating the usefulness of this technique is presented. The potential errors that can result from the use of portable NPT monitoring devices are discussed.