(A) Schematic summary of epitope mapping by FACS analysis using chimaeric IGF-1R/IR receptors. Antibodies binding to IGF-1R, IR and chimaeric receptors are shown as +, whereas lack of binding is denoted by −. The ability of europium labelled mAbs 7C2 (B) and 9E11 (C) to compete with 25 nM unlabelled 7C2, 9E11, 24-60, αIR-3 and control IgG1 for binding to the sIGF-1R was measured as described in Materials and methods section. Results are expressed as a percentage of europium label bound in the absence of competing mAb, and are means±S.D. of three independent experiments performed in triplicate.