The clinical experience and results of NPT recording on three different groups of patients (a group of normals, a group with high suspicion of psychogenic impotence and a group of organic impotence with a well-known etiology) are reported here. A new classification of erectile capacity which is not only based on change in circumference of the penis, but also on duration of complete erection and rigidity of the penis is proposed. The phalloplethysmography, which is based on the REM-related tumescence is a reliable method for discrimination between organic and psychogenic impotence. A rigidity test, however, is essentially for the detection of insufficient rigidity in spite of normal penile expansion during NPT recording.