Crenolanib is an orally bioavailable, selective inhibitor of type III tyrosine kinases with nanomolar potencies against platelet-derived growth factor receptor α (PDGFRα) and PDGFRβ and Fms-related tyrosine kinase 3 (FLT3; IC50s = 11, 3.2, and 4 nM, respectively). It also inhibits medically-relevant mutant forms of these kinases, including the D842V-containing form of PDGFR and D835Y and internal tandem duplication mutations of FLT3, at nanomolar concentrations. Crenolanib is more than 100-fold selective for these kinases over other tyrosine and serine/threonine kinases. It is effective when used in cells and in vivo.