Blood, meat, or fish, or any combination thereof, were ingested by 9 normal volunteers to permit studies of the contained hemes during total gastrointestinal transit. Quantitative analysis of ingested heme and of fecal heme and its degradation products was made possible by a new specific and extremely sensitive test, HemoQuant. The average fecal recovery of hemoglobin-heme from 10 to 36 ml of blood was 88%, as determined in 13 separate studies. All Hemoccult tests remained negative despite greater than 20-fold increases in fecal heme. Up to 83% of the blood heme was converted in the intestinal tract to porphyrins. These porphyrins are included in the HemoQuant, but not in Hemoccult or other leukodye assays. Negligible amounts of heme were found in fish and fowl, and their ingestion led to no significant increase in fecal heme. An average of only 25% of the heme in ingested meat was subsequently recovered in feces. Control fecal values represented an average of approximately 0.5 ml of blood per day. The recovery data obtained show that fecal HemoQuant results reliably reflect the total amount of blood hemoglobin that enters the gastrointestinal tract.