HepQuant tests are new liver tests that are being developed to accurately measure liver function with sensitivity and specificity while being safe and non-invasive. The primary goal of this study is to define the intra-individual reproducibility of the HepQuant tests, that is, to see if a person is given the tests several times that the test results are essentially the same each time. Subjects for this study will include healthy controls and patients with chronic liver diseases. The chronic liver diseases will include hepatitis C virus (HCV) infection and a serious form of fatty liver disease, known as non-alcoholic steatohepatitis (NASH). The HCV and NASH patients will include men and women, and those with early stage and late stage liver disease as defined by the amount of fibrosis observed in their liver biopsies. Once a subject has been enrolled in the study they will be given the HepQuant tests on three separate days within the span of one month. The hypothesis of this study is that HepQuant tests will reproducibly report liver function in healthy controls and patients with all stages of chronic HCV and NASH liver disease and that liver function will decrease as the amount of liver fibrosis increases in the chronic liver disease patients.