Urethro-cystometry carried out on 20 patients with urinary stress incontinence which was clinically apparent gives quite different results if it is carried out using the water manometry technique of Bech-Heidenreich or using a Mikro-Tip technique without perfusion. Comparing the two techniques shows: --little or no difference in the measurement of the functional length of the urethra and the maximum pressure of closure of the urethra. --no difference between the form of the urethral surface at rest and the bladder surface on effort. --on the other hand it shows a very definite difference in the urethral surfaces on effort which depends on the large differences occasioned by the transmission factor. The latter is weak with the Heidenreich method and corresponds to the clinical state; it is raised with the micro-tip method, which contradicts the clinical evidence.