During the acute phase response, there is an increased production and release of certain proteins known as acute phase proteins (APPs) which can be produced by hepatocytes and peripheral tissues such as C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin (Hp), alpha-1 acid glycoprotein (AGP). These proteins have been investigated as markers of various infectious diseases in small animals and the purpose of this review is to update the current knowledge about APPs in infectious diseases in dogs and cats.University of Glasgow, Animal Health and Comparative Medicine, Institute of BiodiversityUniversidade Estadual Paulista, Departamento de Clínica Veterinária, Faculdade de Medicina Veterinária e Zootecnia de Botucatu