Anti-endoplasmic reticulum antibody positive autoimmune hepatitis in children is characterized by the recognition of a single 50,000 MW protein of the endoplasmic reticulum in liver microsomal fractions by their sera. We have developed an enzyme-linked immunosorbent assay technique with rat liver microsomal preparations as the antigen to be used for detection of this disease. Titers obtained may be useful in following the course of the disease and as an aid in determining when therapy can be discontinued. The technique is rapid, sensitive, reproducible, and simple to perform and is easier to manipulate than immunofluorescence or radioimmunoassay techniques.