The transitional cells at the surface of the urinary bladder secrete and bind to their surfaces 1 or more glycosaminoglycans whose presence prevents bacterial adherence to the mucosa. Because it is believed that adherence is prerequisite to infection, we did the current studies to determine whether the antiadherence effect of natural and synthetic glycosaminoglycans prevents infection. We exposed intact rabbit bladders, mucin deficient rabbit bladders, and rabbit bladders treated with sodium pentosanpolysulfate, a similar but synthetic substitute for the surface glycosaminoglycan(s), to bacteria in vivo. We measured infection rates 48 hours after exposure. The infection rate was significantly higher in mucin deficient bladders than in controls (p less than 0.02). There was no significant difference between infection rates in controls and infection rates in bladders treated with sodium pentosanpolysulfate. These results support our impression that a bladder with an intact mucin layer is better able to resist infection than is a mucin deficient bladder. The natural surface glycosaminoglycan(s) and the synthetic substitutes that reproduce their antiadherence effect appear to be protecting factors.