We examined whether mutation of the platelet-derived growth factor receptor protein tyrosine kinase (PDGFR)-α and PDGFR-β genes contributes to their overexpression in canine vascular tumours. Genomic sequences of trans- or juxtamembrane regions of PDGFR-α and PDGFR-β were analysed with immunohistochemical staining and polymerase chain reaction-direct sequencing using DNA from paraffin-embedded neoplastic tissues of 27 hemangiosarcomas (HSAs) and 20 hemangiomas (HAs). Immunohistochemically, 75% of the HA cases were positive for PDGFR-α and almost most of the HA cases were negative for PDGFR-β. Of the HSA cases, 55.6% were negative for PDGFR-α and 63% were strongly positive for PDGFR-β. Among the HA cases, 1 missense mutation was detected in PDGFR-α exon 18 and 1 in PDGFR-β exon 17. Two HSA cases had missense mutations in exon 14 and 1 in exon 17 of PDGFR-β. Thus, genomic mutation of trans- or juxtamembrane regions of PDGFRs was not the main mechanism driving the activation of receptors in HSA and HA.