Cloned antibodies to specific epitopes of hepatitis D virus were produced by transformation with Epstein-Barr virus and subsequent cloning of peripheral blood B lymphocytes from a patient with chronic hepatitis D virus infection. Several stable cloned B cell lines, derived from two parent cultures, produced hepatitis D-virus-specific IgG antibodies. Some cloned IgG antibodies detected hepatitis D virus-associated antigen in hepatitis D virus-infected woodchuck liver tissue sections by indirect immunofluorescence staining and some reacted in an inhibition ELISA test detecting hepatitis D virus antibodies; most cloned IgG lines detected hepatitis D antigen both in immunofluorescence tests and in inhibition ELISA. Cloned antibodies to hepatitis D antigen detected by ELISA and/or immunofluorescence staining recognized the two major specific native and denatured polypeptides, p27 and p29, in Western blot analysis. Such cloned antibodies for hepatitis D virus are potentially useful for clinical diagnosis and research.