60 patients with histologically proven NASH will be randomized to receive either exenatide (2 x 5 µg s.c. for 4 weeks, 2 x 10 µg thereafter) or placebo treatment, in a 1:1 ratio. Liver biopsies will be performed after 24 weeks of treatment. In addition, a non-invasive assessment of hepatic mitochondrial function will be carried-out using a 13C-methionine breath test at baseline, and at weeks 12 and 24. Insulin sensitivity and glucose tolerance will be assessed by a hyperinsulinaemic-euglycaemic clamp (baseline and week 24) and an oral glucose tolerance test (baseline, weeks 12 and 24). Hepatic fat content will be measured by magnetic resonance tomography. Liver enzymes will be monitored closely throughout the study period.