The sera of three children with chronic benign neutropenia, due to anti-neutrophil antibodies, were studied with respect to their antibody specificity. This was done by screening the sera against a panel of leukocyte donors in the EDTA micro-agglutination test and in the indirect fluorescence test. Two of the sera contained antibodies against the known neutrophil-specific antigen NA2. The third serum was directed against a new neutrophil-specific antigen. Genetic analysis showed no correlation between this antigen and the already known neutrophil-specific antigens: 9A, NA1, NA2, NB1, and NC1. In the Dutch population the frequency of the new antigen, tentatively called NE1, is 23%, which gives a gene frequency of 0.12.