The human bile lipoprotein complex includes an apoprotein fraction of IgA fragments and an acidic polypeptide tightly bound to bile cholesterol and phosphatidylcholines. The fate of the intestinal bile lipoprotein complex was immunohistochemically studied. Its localization in the human duodenum is consistent with selective capture or synthesis. The result of both might be the presence of bile apoprotein in the bloodstream. These two mechanisms may explain the cross-reaction between the lipoprotein complex apoprotein and the high density lipoprotein.