A case of Hb H disease from Algeria was studied at the genetic and molecular level in order to delineate the pattern of α-thalassemia in the Mediterranean population. The family study indicated that both parents had the hematological and clinical manifestation of α-thalassemia trait and that the affected sibling had homozygous α-thalassemia with 5.6% Hb H, microcytosis and an α-/non-α-biosynthetic ratio of 0.64. Hybridization in globin cDNAα excess suggested that the molecular defect responsible for this form of α-thalassemia is a partial deletion of the haploid stock of α-globin genes. The Algerian case of Hb H disease studied thus differs from Asian and Negro cases by the mode of inheritance of the α-thalassemia mutation