A disease closely resembling the human neutrophil dysfunction syndromes has been identified in a colony of dogs. The syndrome, referred to as the canine granulocytopathy syndrome, is characterized by recurrent-life-threatening bacterial infections and a greatly shortened life span. The disease is genetically determined, being transmitted as an autosomal recessive trait. The increased susceptibity to pyogenic infections and shortened life span is related to an impairment of leukocyte function at the cellular level. Preparation of neutrophils from affected animals exhibit impaired in vitro killing of Esherichia coli. The defect in bactericidal activity is associated with reduced glucose oxidation by the hexose monophosphate shunt and an increase capacity to reduce nitroblue tetrazolium dye. The data obtained thus far indicate the canine granulocytopathy syndrome will be of considerable value as a model for study of granulocytypathy sydromes in man.