When viewed under a microscope, liver tissue damaged by chronic infection with the hepatitis C virus shows inflammation. As the disease progresses, scarring (fibrosis) occurs. This scarring can eventually cause a condition called cirrhosis, which can lead to liver failure. In some patients, treatment with a drug called interferon eliminates the virus. Doctors can now measure the amount of virus in patients' blood. Patients who have no measurable amount of virus in their blood 6 months after interferon treatment are generally considered to have responded well to the drug. Preliminary studies suggest that patients who respond to interferon treatment have improvements in liver inflammation. It is not known, however, whether fibrosis also improves with interferon treatment.