Three children (girls) suffered from neutropenia mediated by anti-neutrophil IgG-Fc receptor type III (Fc gamma RIII) antibodies. The first patient (newborn) had asymptomatic and transient neutropenia caused by maternal Fc gamma RIII iso-antibodies. The second patient (6 months), whose neutropenia was diagnosed as a 'benign neutropenia of childhood' caused by transient anti-NAI autoantibodies, suffered from mild bacterial infections. The third patient (12 years) suffered from serious infections. The anti-Fc gamma RIII autoantibodies showed neither anti-NA1 nor anti-NA2 specificity. She also developed autoimmune thyroiditis (Graves' disease). Both the duration of the neutropenia and the seriousness of the bacterial infection were variable in our patient group. The first two patients both made spontaneous recoveries, while the third patient depended ultimately on granulocyte-colony stimulating factor (G-CSF).