The frequencies of four malaria associated erythrocyte genetic abnormalities have been established in 1000 Omani subjects. They are: homozygous alpha+ thalassaemia (-alpha/-alpha) 0.45; high Hb A2 beta thalassaemia trait 0.015; sickle trait (Hb A/S) 0.061; and glucose 6 phosphate dehydrogenase deficiency (Gd-): males 0.27, females 0.11. From our data the alpha+ (-alpha/) thal gene (confirmed by Southern blotting) is pandemic in this population. Moreover, in spite of the very high frequency of Gd-, oxidative haemolytic syndromes are very uncommon. Also preliminary data indicate that among the Omani population with sickle cell disease, homozygosity of the alpha+ gene markedly modifies the clinical picture.