Twenty-five of 237 cases of hematuria were classified as unexplained. The patients with this condition were subjected to a battery of 24 laboratory tests, intravenous pyelography, cystourethroscopy, infusion nephrotomography, arteriography, and renal biopsy. Additional diagnostic information was uncovered for 14 patients. Glomerular disease was the probable source of bleeding in ten. Hematuria was cited as secondary to sickle cell trait disease in three. An unusual renal arteriovenous fistula was the cause of bleeding in one patient. Three patients had hyperuricemia. Excretory urography and cystourethroscopy must always be done but nephrotomography, arteriography, and renal biopsy do not have sufficient diagnostic return to warrant routine use in patients with unexplained hematuria. The clinician must weigh (1) the severity of the bleeding, (2) the likelihood of recovery of significant information, and (3) the possibility of serious complications of the tests when he decides whether to employ them in his evaluation.