The transitional epithelium of the urinary bladder secretes and binds to its surface a glycosaminoglycan than inhibits the adherence of bacteria. Synthetic sulfonated glycosaminoglycans instilled intraluminally into bladders whose natural mucin layer has been removed are as effective as the natural mucin in preventing bacterial adherence. It also appears that adherence of calcium and protein is reduced in the presence of both the natural mucin layer and the synthetic sulfonated glycosaminoglycan sodium pentosanpolysulfate, suggesting that the antiadherence activity of both natural and synthetic surface glycosaminoglycans in the bladder extends to the molecular and ionic levels.