The endoscopic treatment of vesicoureteral reflux with transurethral injection of teflon into submucosal part of ureter was performed for the first-time in 1981. Unfortunately this method of treatment was not accepted because of the teflon migration (proved in experimental therapy) into different organs (lungs, brain, lymphatic nodules). Defining the quantity changes of teflon in children treated with this method in long-term follow-up (minimum 8 years). The ultrasonography was performed in 20 cases of female children with diagnosed vesicoureteral reflux and treated in 1987-1990 by injection of teflon (in age from 1 to 10). There were 33 ureters treated. The vertical and transversal sizes and the area of teflon were defined and compared with ultrasonographic investigation performed early after injection. In 14 ureters (43%) the sizes of teflon mass in submucosal part of the ureter were the same as just after injection. In 12 ureters (36%) the mass was considerably lower and in 7 cases (21%) there was no teflon in the injection place. The changes of teflon mass quantity were noticeable in 57%. CONCLUSIONS The reduction or loss of teflon mass injected into submucosal part of ureter in children treated endoscopically for vesicoureteral reflux was demonstrated in high percentage of cases. There is a possibility that teflon was excreted into bladder through mucosa perforated by a needle during injection or because of later perforation of mucosa. This hypothesis is not so probable--early postoperative ultrasound controls showed right quantity of teflon mass. There is no proof that the loss of mass is caused by migration. This situation has to be taken into consideration but the appearance of symptoms is rather not probable (quantity of injected mass varies 0.1-1 ml).