Urodynamic study of 66 patients with caudal injury and of 7 patients who underwent saddle block was evaluated by putting emphasis on the maximal pressure of the urethra (UPmax). The static pressure of 49.7 +/- 10.8 cm H2O in the membranous urethra of the patients with completely paralyzed sphincter raised the question that some active muscle that functions to open the membranous urethra must have been working during physiological urination. Urodynamic findings of detrusor sphincter relationship, monitored by pressure and electromyogram (EMG) measurement, suggested that the combined reflections of the pelvic floor muscle and urethral sphincter are present. We concluded that this would be induced by the transversus perinei profundus muscle contraction and the urodynamic interpretation would be re-integrated on the role of this muscle on active urethral opening mechanism.