We have analyzed the beta-thalassemia mutations in 99 chromosomes of 49 adults with beta-thalassemia major and of one with Hb S-beta-thalassemia, who are regular patients at a large hematology clinic in Baku, Azerbaijan. A total of 20 different mutants were identified; three [frameshift at codon 8 (- AA); IVS-II-I (G --> A); IVS-I-110 (G --> A)] were present in about two-thirds of all chromosomes. Most alleles are the same as found in Mediterranean populations; a few have an Asian origin or come from Kurdistan, Lebanon, Saudi Arabia, or a black population. One mutant [frameshift at codons 82/83 (- G)] might be specific for the Azerbaijanian population. Nearly all patients were transfused, which made quantitation of Hb F impossible; high (G)gamma values were present in the Hb F of those patients whose beta-thalassemia chromosome carried the C --> T mutation at position - 158 in the promoter of the (G)gamma-globin gene.