OC-3-VGH ovarian cancer cell line and numerous others from different human tissue origins were studied for their respective expressions of immunoglobulins as well as carbohydrate-associated epitope(s) recognized by RP215 monoclonal antibody. With no exceptions, all the cancer cell lines studied so far express human immunoglobulin G (IgG) heavy chains when determined by Western blot or nested RT-PCR with appropriate primers in the constant region. By Western blot assay, it was also shown that greater than 90% of cancer cell lines expressed RP215-specific epitope(s) on the detected heavy chain molecules. Further studies with OC-3-VGH cancer cells revealed the expressions of all immunoglobulin classes, subclasses, heavy as well as light chains. The primary structure of the IgG heavy chains expressed by single cloned cells of this cancer cell line was elucidated. It was shown to be homologous to that of normal human IgG1 heavy chain derived from B cells, except with high content of serine/threonine residues in the variable region. Expressions of other immunoglobulin-related genes were also detected. Widespread expressions of immunoglobulin heavy chains among cancer cells as well as the frequent presence of unique carbohydrate-associated epitope(s) recognized by RP215 monoclonal antibody might have important biological implications during carcinogenesis and applications in immunodiagnostics and antibody-based anti-cancer drug developments.