Inclusion Criteria:  For group 1: Patients (age ≥ 21) have established sexual relationship for at least 3 months. These patients are complaining of ED and not responding to intracorporal injections (ICI). For group 2: Men (age ≥ 21) have an established sexual relationship for at least 3 months. These men have normal erectile function.  Exclusion Criteria:  Peyronnie's disease, post-priapism corporal fibrosis, and clinically detected post traumatic corporal fibrosis, previous ICI therapy, history of penile and/or urethral surgery, liver cell failure, renal failure, heart failure, endocrinal diseases (e.g. thyroid- Adrenal), medications that may cause ED, and neurologic and psychotic disorders.