Interstitial cystitis is a chronic bladder disease with certain features that suggest autoimmunity may play a role in initiating or maintaining the disease process. We therefore determined whether immunoglobulin fractions from 14 IC patient and 19 control urine specimens bound in vitro to primary cultures of human bladder epithelial cells, as well as epithelial cells from a variety of other tissues. Urine autoantibodies that bound to normal human bladder epithelial cells were present in 8 of 14 IC specimens (from 6 of 9 IC patients) as compared to 3 of 23 control specimens (from 2 of 17 control patients). These antibodies, which were usually also present at low titers in sera from these persons, bound to at least four nuclear or cytoplasmic antigens, with the specificity of autoantibodies from a given individual varying over time. The autoantibodies were not specific for normal or malignant bladder epithelial cells, but bound to epithelial cells from a variety of tissues. These data show that anti-epithelial cell autoantibodies are present in the urine of IC patients, but suggest that these antibodies are not likely to be a primary cause of this disease.