The serum of 2 patients suffering from autoimmune neutrophil granulocytopenia contained autoantibodies that were directed against a new granulocyte-specific antigen. Genetic analysis showed that this new antigen was not correlated with the already known neutrophil antigens NA(1), NA(2), NB(1), NC(1) or 9a. This was studied in a four-generation family. In the Dutch population the frequency of the antigen, tentatively called ND(1), is 98.5% (n = 67), pointing to a gene frequency of 0.88.