β-Thalassemia is a common disease in Southern China and 10 different mutations or frameshifts are responsible for most types ofβ-thalassemia in this area. We studied 126 chromosomes of 80β-thalassemia patients from the Guangxi, Guangdong, and Sichuan Provinces using the polymerase chain reaction followed by dot-blot hybridization with specific oligonucleotide probes. The most common mutation in the three provinces is the frameshift at codons 41-42, followed by the A→T mutation at codon 17. The A→G mutation at nt -29 of the promoter is common in Sichuan but not in the other two provinces. Three mutations (T→C at nt -30; G→T at IVS-I-1, and G→C at IVS-I-5) were not observed. These data were used to initiate a prenatal diagnosis program using the same techniques for identification. Eleven fetuses at risk forβ-thalassemia have been diagnosed.