One third of the population in the United States has nonalcoholic fatty liver disease (NAFLD). Nonalcoholic steatohepatitis (NASH), the progressive form of NAFLD, can lead to cirrhosis.Currently, there is no proven therapy for patients with NASH. The investigators core hypothesis is that therapy of patients with NASH with pentoxifylline (PTX) for one year will result in improvement of biochemical parameters of liver disease and hepatic histology. The focus of this proposal is on the effectiveness of pentoxifylline (PTX) in improving laboratory and tissue parameters of liver disease, parameters of insulin-resistance, and levels of cytokines in patients with NASH.