Additional alpha-genes may increase the severity of heterozygous beta-thalassemia. Conversely, the co-inheritance of alpha-thalassemia with homozygous beta-thalassemia and the consequent reduction in alpha-globin chain excess often results in a milder clinical and haematological phenotype. This study describes the hematological and the molecular data resulting from the interaction between alpha and beta-thalassemia determinants in a Jordanian family. The parents are double heterozygotes for alpha and beta-thalassemia. DNA analysis of four children characterized homozygosity for beta+ IVS 1.6 thalassemia mutation in three of them. Co-existing heterozygosity for -alpha 3.7 was detected in two of them (Children 1 and 2). Those two children have a less severe clinical course than that of the third child (Child 3) with homozygosity for beta-thalassemia only. The co-existence of -alpha3.7 mutations with homozygous beta-thalassemia may have converted a transfusion-dependent thalassemia major to non transfusion-dependent thalassemia intermedia. The fourth child (Child 4) was heterozygous for -alpha3.7 but lacked beta+ IVS 1.6 mutation and appeared normal.