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Glucagon like peptide 1 (GLP-1) is an intestinal hormone that plays an important role in glucose metabolism. GLP-1 is released from mucosal L-cells following nutrient ingestion and contributes to the incretin effect, the enhancement of insulin secretion occurring with enteral compared to intravenous glucose administration. The mechanisms linking nutrient absorption and GLP-1 secretion are unknown and studies addressing this topic, particularly in small animal models, have been hampered by the relatively low concentrations of GLP-1 in the circulation. We hypothesized that GLP-1 levels would be higher in samples of intestinal lymph compared to plasma and could provide a novel system in which to study meal-induced hormone secretion. We addressed this hypothesis in conscious rats with indwelling catheters in the portal vein and distal intestinal lymph duct. These animals had plasma and lymph sampled before and for 240 minutes after instillation of a liquid meal into the gastrointestinal tract. Lymph contained detectable concentrations of glucose, insulin, and GLP-1 that was reliably measured using our assays. Before and after the Ensure feeding plasma insulin levels were approximately twice as high in portal plasma as intestinal lymph. In marked contrast, GLP-1 level