SUMMARYCorynebacterium jeikeiumcauses septicaemia in neutropenic patients usually after colonizing intravenous lines. This paper reports the results of immunoblotting sera from 14 patients with aC. jeikeiumsepticaemia. Recovery from the septicaemia was associated with production of both IgM and IgG against antigenic bands of 50, 52 and 110 kDa. Antibody against the 110 kDa band was present in controls but the antibody against the 50 and 52 kDa was specific to those patients who had on-going or previousC. jeikeiuminfection. A case ofC. jeikeiumendocarditis is also presented and here recovery was associated with seroconversion to the 50 and 52 kDa bands.