Pharmacokinetic investigations of bilirubin resorption by the intestine of Gunn rats have shown that the excretion of bilirubin is markedly dependent upon the frequency of defaecation. The serum bilirubin concentration is strongly affected by obstipation or diarrhea, so therefore the influence of diet upon this parameter in Gunn rats was investigated. Not only natural breast milk but also adapted milk strongly inhibited the resorption of bilirubin. This cannot be attributed to an increased defaecation frequency. Instead it is postulated that the resorption of bilirubin is hindered due to a masking effect of the fat present in the nutrient.