Fat necrosis and arthritis occur in some individuals with pancreatitis. The intraarticular free fatty acid concentration was found to be markedly elevated in 2 patients with this pancreatitic arthritis syndrome. Injection of free fatty acids into rabbit knees reproduced the inflammatory synovial response including intracellular fat globules within leukocytes. Free fatty acids exceeding the available binding sites of albumin appear to mediate the extrapancreatic inflammatory manifestations of this syndrome.