In an ongoing home screening study 231 men 50 or more years old without known causes of hematuria have tested their urine each week with a chemical reagent strip for the presence of blood. After 3 months of testing 23 patients have had hematuria at least once. Of these men 5 have had urinary cancers and 5 have had other serious underlying diseases requiring immediate treatment. In only 3 of these 10 men (only 1 with cancer) did hematuria occur in more than a third of the testings or on subsequent microscopic urinalysis. The degree of hematuria was unrelated to the seriousness of its cause. We conclude that in this population hematuria occurs so intermittently that when found on routine urinalysis, regardless of quantity, serious underlying pathological conditions must be ruled out aggressively. Furthermore, regular hematuria home testing appears to offer promise as an economical means to detect urinary cancers and other serious diseases in asymptomatic men 50 or more years old.