It is now recognized that screening for fecal occult blood is useful to alert the clinician to possible colon cancer in an early stage. The guaiac impregnated card is not widely used because patients must maintain strict diets omitting red meat, peroxidase-containing foods, iron supplements, and ascorbic acid. The Hemo-matic Analyzer uses a special filter to adsorb fecal Hb which is then automatically washed free of interfering substances and quantitatively identified. The filter electrostatically binds Hb and not pepsinized blood or substances that interfere with occult blood testing. We evaluated the sensitivity of this device and compared it to the Hemoccult II test in vivo and in vitro. It was approximately six times more sensitive than Hemoccult II and was not influenced by the presence of ascorbic acid, plant peroxidase, or ingestion of a large quantity of rare red meat. In addition, the samples remained positive more than 10 wk after preparation. The Hemo-matic Analyzer is a useful new device that offers many advantages over Hemoccult card testing for screening for colon cancer.