β-glucuronidase hydrolyzes glucuronic acid from bilirubin glucuronides. The unconjugated bilirubin that results is more readily absorbed from the intestine. Human breast milk has significant β-glucuronidase activity, and it has been suggested that the milk may play an etiologie role in the hyperbilirubinemia commonly seen in breast-fed infants. To test whether breast-milk can facilitate intestinal bilirubin absorption, pairs of rats were fitted with bile duct and duodenal catheters. One rat of each pair received an intraduodenal infusion of rat bile plus breast-milk; the other rat received a similar amount of bile and milk plus the β-glucuronidase inhibitor saccharolactone. Rats receiving saccharolactone excreted significantly less bilirubin in their bile, suggesting that inhibition of 0-glucuronidase decreased intestinal absorption of bilirubin. These findings were not seen in similar experiments when saline was substituted for human breast-milk.