On the basis of DNA from a beta-thalassemic patient, human gene library has been obtained using bacteriophage lambda EMBL4 as a vector. The recombinants contain human DNA insertions of 15 to 20 kb. The lambda A1 beta 1 clone has been isolated by the method of hybridization of phage plaque replicas to the HhaI fragment of JW102 plasmid containing human beta-globin cDNA. Restriction mapping revealed the presence of a 22 kb human DNA fragment comprising a portion of the beta-globin gene system. Subcloned fragments of beta-globin gene (within the pUC19 plasmid or phage MI3mp10) were sequenced using the Maxam and Gilbert method as well as that of Sanger. 2150 nucleotides in total were analysed. We have detected the point substitution G----A in the 110 nucleotide of minor intron, leading to the formation of an additional splicing site.