His research has concentrated on the pathogenesis of NASH, NRH, FNH, and the role of vascular events in the pathogenesis and regression of cirrhosis. His studies were the first to document the role of insulin and hyperinsulinemia in human fatty liver disease, providing insight into the pathogenesis of fatty liver occurring in obesity (NASH), alcoholism, and post-jejuno-ileal bypass. He demonstrated how heterogeneity of insulin delivery to the tissues explains focal fatty change and focal fatty sparing. His studies of the hepatic vasculature provide insights for the pathogenesis of focal nodular hyperplasia, nodular regenerative hyperplasia, non-cirrhotic portal hypertension, and cirrhosis.