Abstract: The histochemical and biomarker for liver fibrosis is a technique for determining the existence and extent of liver fibrosis by evaluating the extent of peptidylarginine deiminase (PAD) activity by immunological methods. The method is illustrated using liver biopsy. A small section of tissue from a liver biopsy is incubated overnight with a monoclonal antibody specific to PAD, stained, and examined microscopically. The number of hepatocytes that positively express PAD activity per one hundred hepatocytes is counted and expressed as a percentage. The percentage of PAD activity is then correlated with a METAVIR fibrosis score according to results from a statistically significant reference population. The degree of liver fibrosis and an appropriate treatment regimen may then be determined.