Further insight into the physiology of erection acquired in recent years had led to the development of new methods that have enhanced the evaluation of erectile dysfunction. These new methods will permit a more precise diagnosis and, consequently, the management of this condition can be based on scientific and not empirical methods. To date, many questions remain unanswered and many points have not been elucidated. Using a precise methodology will permit us to corroborate or correct what has been done up until now and to develop new methods of investigation. The present study briefly reviews the physiology of erection and describes a method we routinely use.