The extracellular domains (ECD) of epidermal growth factor receptors, ErbB1, 2, 3 and 4, were designed as soluble dimeric forms. Each ECD was fused to a short hinge region derived from IgG, such that the stable dimer could be formed with disulfide bridges. This hinge-tagged design minimized the molecular weight to approximately 50% of the conventional Fc-fusion design without an Fc domain of IgG. The refolded dimers could be easily analyzed and characterized by SDS-PAGE. Hinge-tagged soluble ErbBs demonstrated significant affinity for betacellulin and heregulin. The IgG hinge-tag should be a simple method to design soluble dimers that would be useful for high throughput screening of ligands, antagonists or derivatives.