CD16 antibodies recognize Fcgamma receptors III of a and b types. In a patient with severe idiopathic aplastic anaemia (AA), polymorphonuclear cells, which in normal subjects express FcgammaRIIIb, were found to be CD16 negative. The FcgammaRIIIb gene configuration was analysed by PCR on peripheral blood mononuclear cells. Bi-allelic deletion encompassing at least part of the coding exon 5 was found in the patient and his brother, suggesting a hereditary defect. The patient underwent successful bone marrow transplantation from his HLA-matched brother despite a similar phenotype and genotype. This observation suggests that FcgammaRIIIb hereditary deficiency in donor and/or recipient does not impair engraftment and justifies the use of other monoclonal antibodies in addition to CD16 in the study of GPI-anchored antigen expression.