A cat with epitheliotrophic T-cell lymphoma with paraneoplastic eosinophilia is described. Initial attempts to control the disease with conventional therapies failed. The addition of recombinant human interferon α2b (rhINFα2b) resulted in a clinical, haematogenous and sonographic improvement for 49 days. The overall survival time from initial diagnosis was 100 days. Relapse was correlated with the development of serum antibodies directed against rhINFα2b. To our knowledge, this is the first report describing the clinical use of IFNα in the treatment of neoplasia in the cat.