We report here a new frameshift mutation in exon 3 of the β-globin gene, a single nucleotide deletion (-C) in between codons 140/141 (GCC/CTG→GCC/TG), found in an 8-year-old Argentinean girl with clinical picture of thalassemia intermedia. It leads to a β-chain that is elongated to 156 amino acids [(141)Trp-Pro-Thr-Ser-Ile-Thr-Lys-Leu-Ala-Phe-Leu-Leu-Ser- Asn-Phe-(156) Tyr-COOH]. 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