Eosinophil cationic protein (ECP) is currently used as a biomarker for airway inflammation. It is a heparin-binding ribonuclease released by activated eosinophils. Its cytotoxicity toward cancer cell lines is blocked by heparin. The objective of this study was to locate the heparin binding site of ECP by site-directed mutagenesis and construction of a synthetic peptide derived from this region....