AbstractPorcine aortic endothelial cells expressing platelet-derived growth factor (PDGF)α- orβ-receptors after transfection of the corresponding cDNAs, were used to investigate whether PDGF receptor dimerization occurs in intact cells after ligand binding. Using three different methods—covalent cross-linking of125I-labeled ligand, cross-linking of metabolically labeled cells after ligand-binding followed by immunoprecipitation, and immunoblotting of cells after ligand binding and cross-linking—it was demonstrated thatα- as well asβ-receptors form ligand-induced dimeric complexes. Dimerization correlated with induction of receptor kinase activity, measured as receptor autophosphorylation. Heterodimeric complexes could furthermore be induced by PDGF-AB, when added to a mixture of lysates from theα- andβ-receptor expressing cell lines, or when added to human fibroblasts which express both receptor types.