In this study we report for the first time the distribution of human platelet alloantigens (HPA) in Saudis. These antigens are implicated in the pathophysiology of alloimmune thrombocytopenia. We collected blood samples from 84 healthy male Saudi blood donors. DNA isolated by salting-out and ethanol precipitation was amplified for genes HPA 1-5 using the polymerase chain reaction/sequence specific primer method. We found high HPA-1 polymorphism similar to Caucasians. HPA-4 polymorphism in Saudis was, however, greater than in Caucasians, and more similar to that of the Japanese. These results suggest that both these two HPA systems may be clinically important in Saudis.