We have studied the spectrum of mutations producting beta-thalassaemia intermedia in South China. The methods of mutation detection include oligonucleotide analysis, polymerase chain reaction amplification of the beta-globin gene and direct genomic sequencing. The mutations have been identified in 22 beta-globin genes from the patients in 11 unrelated families. Seven different mutations have been identified and the A to G substitution in the TATA box of the beta-globin gene accounts for 42% of these mutant beta-globin genes. Most patients have a beta(+) thalassaemia and one copy of the TATA box mutation. In two patients with beta(0) thalassaemia intermedia the mild phenotype may be explained in one by the presence of the - + - + + 5' beta-globin gene cluster haplotype which contains the Xmn I site -158 nt to the G gamma-globin gene or in the other by the number of alpha-globin genes present.