A strong antibody was found in a mother (first pregnancy) who had a severe neutropenic baby. The father's granulocytes were typed by flow cytometry as NA1+, NA2+, NB1+, ND1+ and the mother as NA1-, NA2+, NB1+ and ND1+. The antibody was identified as anti-NA1 by us, and confirmed later by a reference laboratory. The serum reacted with 54.8% of the 31 donors tested. The same antibody was found in the child's serum 35 days after birth, and the reactivity was stronger than in the mother's serum. The HLA-DR, DQ from the mother was DR3, DR7; DR52, DR53; DQ2. The baby's granulocytes were recovered slowly over a four-month period, but the course was benign without any specific treatment. Five months after birth, with recovery, the child's serum became negative and his granulocytes were confirmed as NA1+. Due to the difficulties in fully diagnosing and working with granulocytes we suspect that there are undetected cases; only one case has been recorded in Spain before.