The role of urine in the etiology of cancer of the urinary bladder.

It is shown that the site-frequency distribution of carcinomas relative to the upper and lower hemispheres of the urinary bladder is inhomogeneous. It is pointed out that the contact with urine is the important etiological factor and that other factors, if any, play only a secondary role. It is suggested that prolonged (forced) retention of urine should be avoided. Investigation of urinary carcinogens is needed.