All healthy men experience penile enlargement during nighttime sleep, which is a normal physiological phenomenon that is not affected by psychological factors, due to the erection of the penis caused by the transmission of impulses from the central nervous system. The average number of erections is more than 3 times/night and the total erection time is about 100 minutes. Using this principle, the nocturnal penile tumescence (NPT) test has been designed for the following purposes: to distinguish between erectile dysfunction (ED) caused by psychological factors or organic pathology; forensic evaluation, etc. Patients: The subject has an erectile dysfunction condition and needs to be analyzed for etiology. Method: The patient should sleep naturally in the monitoring room for one night, wear disposable electrode patch on the corresponding area, and tie the recording box on the thigh. Monitoring indicators include: the number of erections, duration, length and circumference of the penis, and changes in blood volume. Note: (1) the subject should make an appointment for the examination; (2) the subject should shave the penis body, penis root and right hip before coming to the hospital for examination; (3) the subject should explain to the physician before the examination whether he/she has symptoms of anxiety, depression or even frequent insomnia; (4) he/she has a history of taking sleeping pills and other medications; (5) the subject should explain to the physician his/her sleep habits and sleep quality, such as being more active during sleep.