A 4.4-kb PstI fragment containing the entire β-gene of the human β-globin gene cluster plus both 5’- and 3’-flanking sequences was used as a probe to study the chromosomal localization of the β-gene by in situ hybridization. Using random oligonucleotides as primers, the β-gene DNA was 3H-labeled with the large fragment of DNA polymerase I (Klenow fragment) to a specific activity of 1.2 × 108 cpm/µg. Almost 80% of hybridization grains observed were located on the distal short arm of chromosome 11. High-resolution chromosome analysis suggests a more precise location of the β-gene to region 11p