In a retrospective review, 52 patients with interstitial cystitis have been studied. Patients with persistent lower tract irritative symptoms, repeatedly sterile urine, and negative urine cytology must be suspected of having interstitial cystitis, and a diagnosis of urethral syndrome in such patients is highly questionable until cystoscopy under anesthesia has been performed. We believe that the finding of multiple petechia-like hemorrhages (glomerulations) on the second distention of the bladder is the hallmark of interstitial cystitis, and that a reduced bladder capacity and a Hunner's ulcer represent a different (classic) stage of this disease. In all stages, the characteristic histologic finidng is submucosal edema and vasodilation. The presence of eosinophils and mast cells is variable, and even in the classic disease the muscularis often appears to be normal. Immuno fluorescent studies and laboratory tests, including the fluorescent antinuclear antibody test (FANA), have not helped us to diagnose (or investigate) interstitial cystitis. Bladder instillations with a 0.4 per cent solution of oxychlorosene sodium (Clorpactin WCS-90) have provided remarkable relief for many patients with this disease, particulary those with the classic form.