Antisera to a variety of nongenitourinary tissues (pancreas, submaxillary gland, liver and heart) revealed numerous constituents in normal human urine. By the methods used, these urinary antigens were not related to plasma proteins, and in the case of antipancreas and antisubmaxillary gland sera, several of them apparently were also not derived from kidney, or from the remainder of the genitourinary tract. The evidence suggested that some of these urinary antigens may have originated in nongenitourinary tissues, entered the circulation in trace quantities, being preferentially concentrated and excreted by the kidney into the urine. Urine concentrates appeared to be relatively enriched in several of the ‘tissue’ antigens detected with these antisera, as compared to extracts of the tissue used for immunization. Five of the urinary ‘tissue’ antigens were found to possess enzyme activities (esterase, phosphatase, cystine-amino-peptidase, glucosaminidase and glucuronidase). Their organ distribution was variable, ranging from presence in all the tissues tested, to detection only in urine.