Platelet glycoprotein (GP) Ib from healthy individuals from the United States was analyzed using SDS-polyacrylamide gel electrophoresis and staining with peanut agglutinin-coupled peroxidase or wheat germ agglutinin-coupled peroxidase after transfer of electrophoresed proteins to nitrocellulose. The GPIb from American Caucasians (109 individuals) was found to be polymorphic, showing types A, B, C, and D of GPIb, similar to what was observed in Japanese. The phenotype distribution pattern, however, was very different from that observed in the Japanese population. GPIb heterogeneity was also observed in American Blacks, Asian Americans, and Americans of Hispanic origin. Thus, it appears that the polymorphism of GPIb is a general phenomenon which should be regarded as an important factor when doing studies on this glycoprotein.