In order to delineate the spectrum of beta-globin gene defects causing beta-thalassemia in the Oran region of Algeria, we have analyzed a representative sample of 31 beta-thalassemia patients. This led to the detection of 10 mutations. Four of them [nonsense codon 39 (C->T), IVS-I-110 (G->A), IVS-I-2 (T->C), and frameshift codon 6 (-A)] account for approximately 77% of the beta-thalassemia chromosomes. Three of these mutants are also widespread in Mediterranean populations, whereas the fourth, IVS-I-2 (T->C), appears typical of the Oranese population. The six other variants are less frequent. The possible origin of these mutated alleles, either by recurrent mutational event or by migration from other populations, is discussed.