Summary—The Specific Red Cell Adherence Test (SRCAT) has been modified to produce clearer, more consistent, permanent preparations. Normal urothelium, inflammatory lesions, squamous metaplasia, papillomata, flatin situand papillary tumours and invasive neoplasms of the bladder have been studied. Inflammatory and squamous changes did not corrupt the test results. The SRCAT was found to be a highly significant test for identifying those patients at risk from invasive bladder tumour. ABH antigens in carcinomain situappeared to be non‐uniformly distributed throughout the bladder urothelium; it is suggested that all subsequent biopsies from these patients should be tes