Rats with bile fistula were injected intravenously with single doses of hematin (5,10,20,30, and 40 mg/kg body weight). Bile samples were collected every 30 min. for 4 hours, and at longer time intervals thereafter. The concentration of hematin in the bile was measured spectrophotometrically at 590 nm. The maximal hematin concentration in the bile (0.29 mg/ml for 40 mg/kg) observed 1.25 hours (average from 15 rats; range 0.5 - 1.5 hours) after hematin administration occured progressively later for lower doses of hematin, and for 5 mg/kg was observed at 3.14 hours (average for 4 rats; range 2-4 hours). The total hematin excreted within 4 hours was 8.0% of injected dose for 40 mg/kg and is dose dependent.