We describe a man with common variable immunodeficiency and polyarthritis. He had suffered several infections, including septic arthritis. For this reason we commenced treatment with antibiotics without obtaining a good response. Three weeks' later, and after knowing that the results of all the cultures were negative, we discontinued the antibiotic therapy and started treatment with indomethacin. A dramatic response was rapidly observed. We feel that an arthritis in a patient with a history of previous infections should alert us to the diagnostic possibility of primary antibody deficiency.