Classical cross-linking technology has been found to be of very limited use in identifying solubilized receptors. A new assay based on the use of heparin-Sepharose was developed here for detecting receptors of fibroblast growth factors (FGFs) in detergent-soluble fractions. This new cross-linking assay is based on the heparin-binding properties of FGF. To this end, solubilized FGF receptors were cross-linked to radiolabelled acidic FGF on heparin-Sepharose. Standardization of the method was carried out by using: 1) crude CHAPS-soluble extracts from chinese hamster ovary cells which express human FGF receptor cDNA (FGFR-2); 2) CHAPS-soluble fractions purified by affinity chromatography from bovine retina. This approach might be a valuable tool for detecting receptors of all heparin-binding growth factors.