Three related Irish wolfhound dogs less than one year old presented with a history of chronic nasal discharge and signs of lower respiratory tract disease. These responded well to treatment initially but were chronically recurring. Cursory evaluation of the immune system (full blood counts, globulin determination and fractionation, electrophoresis and lymphocyte blastogenesis) seemed to indicate a cell-mediated immunodeficiency which, because of the age of the patients, is strongly suspected to be primary.