Uptake by gut epithelial tissue of 60 nm polystyrene particles was studied in female Sprague-Dawley rats (180 g, 9 weeks old) after 5 days oral dosing by gavage (14 mg/kg). The gut was divided into lymphoid and non-lymphoid tissue of the small and large intestine, prior to analysis for polystyrene by gel permeation chromatography (GPC). Approximately 10% of the administered dose was recovered from the entire gastrointestinal tract. The total percentage of the administered dose taken up through lymphoid tissue was statistically much greater than through non-lymphoid tissue. It was estimated that 60% of the uptake in the small intestine occurred through the Peyer's patches, even though the patches comprised a small percentage of the total surface area of the small intestinal tissue. A significant amount of the total uptake was shown to occur in the large intestine, particularly in the lymphoid sections of this tissue. These results were confirmed by fluorescence microscopy.