The concentration of manganese in the duodenum of three steers was increased by infusing manganese chloride intraduodenally at approximately 100, 515 and 840 μmol per minute for 30 hours and the rate at which manganese was excreted in bile was measured. In one steer an infusion of manganese chloride at 529 μmol per minute was toxic and in two steers infusions at approximately 840 μmol per minute were also toxic, causing inappetance, a reduced bile flow and abdominal discomfort. The maximum rates at which manganese was excreted in bile during the first three hours of the infusions at 515 and 840 μmol per minute were between 2.1 and 3.6 per cent of the rate of infusion. During the last three hours of all nontoxic infusions the rate of excretion of manganese in bile was 0.82 ± 0.08 per cent of its rate of infusion. Systemic plasma manganese concentrations did not increase during these infusions. In a fourth steer the longer term capacity of the liver to excrete manganese in bile when the manganese chloride was given intravenously was measured, the concentration of manganese in the portal vein being increased by infusions of manganese chloride solution into a mesenteric vein. The rate of infusion was increased at hourly intervals. The liver’s capacity to remove all manganese during first pass was only exceeded at an infusion rate of 84 μmol per minute. Infusions could be made into the mesenteric vein at 24 and 35.8 μmol per minute for 53 and 26 hours respectively before signs of toxicity were observed. Following signs of toxicity the excretion of copper in bile was decreased for two days.