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The glycoprotein Ib (GP Ib) is the major sialoglycoprotein on the platelet membrane and plays an important role in primary hemostasis. It was demonstrated that GP Ib is polymorphic: four different species of GP Ib (designated A, B, C and D) were observed, having molecular weights of 168, 162, 159 and 153 kiloDaltons, respectively. The polymorphism was first studied in the Japanese population and, subsequently, in Americans; a significant difference between the phenotype frequencies in the two populations was found. The authors report about GP Ib polymorphism patterns in the Italian population. GP Ib from normal subjects was analyzed by means of platelet protein SDS-PAGE followed by Western blotting; GP Ib species immobilized onto nitrocellulose filters were coupled with wheat germ agglutinin and stained using immunoperoxidase. Despite some differences in phenotype distribution, statistical analysis did not show differences between Italian and U.S. Caucasian phenotype frequencies: this is attributable to rather similar gene frequencies in the two populations. In our platelet samples we only observed three GP Ib types, precisely the B, C and D types; therefore we can confirm the rarity of the A type in Caucasians, while it was well represented in the Japanese population.