Recombinant antibody fragments represent useful tools for cancer diagnosis and therapy. Aberrant expression of the HER2 receptor is implicated in metastatic breast and ovary cancers, two malignancies with a high prevalence in young women. In this study, we focussed on a single-chain fragment of variable antibody regions specific for HER2 (scFv8OOE6) that can be expressed in a functional form in the cytoplasm of Escherichia coli. ScFv8OOE6 was extracted from bacterial cultures following induction at different temperatures and purified. The yield of both soluble and insoluble forms was measured. We found that scFv8OOE6 was functional when expressed in the soluble fraction in the bacteria cytosol. In addition, scFv8OOE6 extracted from inclusion bodies was easily refolded and largely recovered its functionality. Thus, scFv8OOE6 is intrinsically capable of efficient and functional folding in a reducing environment and represents one of the few described antibody fragments with a framework well adapted for cytoplasmic expression. (c) 2005 Elsevier Inc. All rights reserved.