Abstract.A 12‐month‐old child neutropenic since the age of 8 months, was referred to our institute for a sepsis fromCandida albicans.On exploring the cause of neutropenia, an anti‐NA1antibody could be detected in the patient's serum. This antibody seemed to be responsible for the neutropenia because the child's PMN type was NA1+. The reactivity of the autoantibody with the patient's own granulocytes was confirmed by direct and indirect immunofluorescence studies performed on blood and marrow cells. A reduced number of T lymphocytes with poor PHA responsivity has been interpreted as the possible cause of the autoimmune disease. Steroid therapy did not cure the neutropenia but the child's general condition imp