A patient with thrombocytopenia and large platelets was discovered to have absent platelet membrane glycoprotein Ib-IX complex by flow cytometry. DNA was isolated from his peripheral blood leukocytes and glycoprotein IX gene sequences were amplified and sequenced, revealing a new mutation. His parents DNA was also isolated and sequenced, and both are heterozygotes for this mutation. More than 100 healthy subjects have been studied for this polymorphism, and a manuscript has been submitted for publication.