AbstractTo determine the feasibility of liver biopsy immunotyping to characterize hepatic lymphoid malignancies, we employed a panel of monoclonal antibodies on snapfrozen hepatic tissue from 18 patients. Six patients proved to have a histologic diagnosis of lymphoid malignancy. By using free avidin and biotin‐blocking reagents to block endogenous biotin, followed by standard immunochemistry, immunotyping was successful in all six cases. Serial section typing allowed delineation of complex B cell phenotypes. Furthermore, architecture was preserved allowing discernment of disease patterns (e.g.), sinusoidal, hairy cell leukemia vs. portal, follicular small‐cleaved cell lymphoma. Unexpectedly, we found striking expression of common ALL antigen in normal bile canaliculi, which may prove of diagnostic or therapeutic relevance. This study establishes the utility of immunohistochemical techniques applied to hepatic biopsies as a valuable adjunct to histologic diagnosis as well as a tool in revealing the immunobiology of the li