Absorption of lead is known to be enhanced during infancy. In this study, the sites of intestinal accumulation of Pb by suckling rats have been determined under various conditions using 203Pb as a tracer. When 203Pb was administered intragastrically (IG) as a soluble salt, accumulation occurred primarily in the duodenum, regardless of dose and vehicle. In contrast, when rat pups suckled from a dam which had received 203Pb, the only region of the small intestine showing accumulation of radioactivity was the ileum. To confirm that these differences were not related to the route of administration, rat milk was labeled with 203Pb and was then used for IG administration. Once again, accumulation (4 hr post-administration) was confined to the ileum. When the dose was increased 10-fold, milk Pb displayed some accumulation in duodenal tissue, but very much less than that of soluble Pb at the same time and dosage. At 20 hr postadministration, there was negligible 203Pb in any region of the small intestine following administration as a soluble salt, but substantial retention in ileal tissue following administration in milk. The strikingly different patterns of intestinal accumulation obtained with Pb salts as compared with milk Pb suggest different modes of absorption of Pb ingested in these two forms.