We constructed a single-chain immunoglobulin in which the carboxyl end of the heavy chain variable domain is covalently joined to the amino terminus of the light chain variable domain via peptide linker and the carboxyl end of the light chain variable domain is linked to human ${gamma}1$ Fc region through the hinge region. The molecule was expressed in Chinese hamster ovary cells, assembled into a dimeric molecule and secreted into the culture medium. The dimeric molecule (2E11) was purified from the culture supernatant by affinity chromatography on Protein G-Sepharose column. The size of the unreduced or reduced protein was the expected molecular weight of approximately 120 or 60 kDa, respectively, as assessed by SDS-polyacrylamide gel electrophoresis. The antigen-binding affinity of 2E11 was almost the same as that of a native antibody counterpart (CS131A), suggesting that the single-chain immunoglobulin may function like a native antibody.