The transport of triacylglycerol (TG) in mesenteric lymph was studied in rats with duodenal and mesenteric lymphatic cannulas with or without bile fistulas. Rats were infused with 135 mumol glycerol trioleate (TO) for 4 h, followed by 5 h of NaCl infusion. Rats with intact fistulas prefed 20% corn oil had nearly twice the maximum output of TG in lymph as controls. Decay from peak values was zero order for controls and indeterminate for rats prefed corn oil. In rats with bile fistulas, less TG was transported in lymph than in those in which 2 mM phosphatidylcholine (PC) was added to the infusate. The decay from maximum values was zero order for controls and first order for rats infused with PC and TO. Recovery of infused [3H]glycerol trioleate in controls was 43% and increased to 68% on inclusion of PC in the infusate. We conclude that in chow-fed rats lymph TG delivery rates were well below infusion rates, suggesting alternate TG transport routes, TG transport was improved by supplementing the infusate with PC or prefeeding with 20% TG in chow, and PC may be limiting in TG transport in rats with bile fistulas.