Clinical evidence suggests that in many settings hypertriglyceridemia can initiate an episode of acute pancreatitis. Hydrolysis of triglycerides by pancreatic lipase with the local release of large quantities of free fatty acids (FFAs) has been proposed as the pathogenetic mechanism. To gather information to evaluate this mechanism an isolated, ex vivo, perfused pancreatic preparation was used. Control preparations remained normal in gross appearance, gained little weight (18 gm), extracted oxygen and glucose and released carbon dioxide, and continued to secrete during a 4 hour perfusion period. Serum amylase remained normal (972 CU/100 ml) as did FFAs (1.11 mEq/liter). When triglycerides were added to the perfusate to increase the serum triglycerides to 1,600 mg%, the glands became edematous, hemorrhagic, and gained considerable weight (52 gm) during the 4 hour perfusion period. Serum amylase became markedly elevated (2,624 CU/100 ml), as did the serum FFA (29.19 mEq/liter). When FFAs were added directly to the perfusate, the glands became edematous, hemorrhagic, and gained weight (90 gm), but did so much more rapidly than when triglycerides were added. These studies add support to the concept that hypertriglyceridemia can initiate pancreatic injury. Furthermore, they suggest that the mechanism may be through the release of FFAs.