Stress incontinence has been said to occur as a consequence of a low urethral pressure and defective pressure transmission from the abdomen to the urethra due to descent of the bladder neck area. Equipment suitable for dynamic pressure measurements has been used to analyse the losses of urethral pressure that lead to incontinence. The pressure transmission from abdomen to urethra was found to be incomplete in both continent and stress-incontinent women. There was also significant loss of smooth muscle tone in the urethral wall after repeated straining, leading to a still narrower margin between the urethral pressure and the leakage treshold in both continent and stress-incontinent women. The main factor determining the degree of continence or incontinence seemed to be the urethral closure pressure at rest . As long as this pressure is sufficiently high, leakage during sudden stress will not occur.