Paraneoplastic eosinophilia is reported in dogs, cats, and humans. Hyp
ereosinophilia (an eosinophil count greater than 1.5 X 10(9) L) is oft
en associated with metastasis and a poor prognosis. This report descri
bes a case of paraneoplastic hypereosinophilia in a pony. Neoplasia sh
ould be included in the differential diagnoses in a horse with eosinop
hilia.