The percentage of Hb S in hemolysates from 109 Saudi Arab males was found to range from 18–47%, with a mean of 33%, an obvious mode at 32–34% and clear skewing of the overall pattern toward lower values. A tentative explanation of this finding is the concurrence of the α-thalassemia trait in this population, which tends toreduce the percentage of Hb S in erythrocytes of double heterozygotes