The method of experimental megaureter modelling in dogs that is based on the operative damage of the ureter segment is described. Obstructive megaureter was found in 100% of "devitalization" of the ureterovesical junction and in 59% of "devitalization" of the middle third of ureter. Progression of megaureter symptoms and reduction of evacuator-secretory function on the side of modelling operation without anatomical narrowing of the ureter lumen in 41% of experiments pointed to the actual role of the functional obstruction in pathogenesis of this hard syndrome. In vitro methods demonstrated the decrease of contractility of the "devitalized" fragments and also of above and below situated segments of megaureter. Urodynamic investigations showed the signs of the bioelectrical disturbance in the megaureter wall and the disorder in excitement and contraction of the megaureter, deterioration of the reactivity of the megaureter on the functional loading tests.