The direct evaluation of the autonomic nervous system to detect the neurogenic component of erectile dysfunction in men is not possible. Biothesiometry, a vibration perception test, is a simple method for the assessment of the penile somato-afferent system. A nomogram for the evaluation of somato-afferent system has been developed utilizing the biothesiometer in healthy men. This nomogram was used to compare the biothesiometric values of potent and impotent diabetic patients. According to our data, the radix penis is selectively damaged by diabetes mellitus in the first stage of the disease, whereas the glans penis is damaged later on when the disease reaches the stage of impotence.