Hematological and hemoglobin composition data, and results from extensive gene mapping, using a battery of restriction enzymes and probes, have been used to distinguish different types of hereditary persistence of fetal hemoglobin (HPFH) (or delta beta-thal) among three Chinese families from the southern part of China. The first (Family Z) is an A gamma-(delta beta)+-HPFH without a detectable deletion and may be the same as, or similar to, that described by Farquhar et al (Am J Hum Genet 35:611, 1983). The second (Family C) resembles a G gamma(A gamma delta beta)o-thalassemia and is characterized by a large deletion of DNA originating 3' to the G gamma globin gene and extending beyond sequences recognized by the pRK28 probe. Data from various digests indicate possible differences in the 3' end of the deletion when compared with data for some other types of G gamma(A gamma delta beta)o-thalassemia, described by Trent et al (Br J Haematol 57:279, 1984). The third (Family Zh) concerns a G gamma A gamma(delta beta)+-HPFH, which is characterized in heterozygotes by a fetal hemoglobin level of 20% to 25% with a G gamma value averaging 60% and by the absence of any DNA deletion detectable by extensive gene mapping analyses. The C----G mutation at position 202 5' to the G gamma globin gene [characteristic for the high G gamma-(delta beta)+-HPFH (Proc Natl Acad Sci USA 81:4894, 1984; Blood 64:1292, 1984)] was absent, but the Xmn I site at position 158 5' to the G gamma globin gene [characteristic for a modest increase in G gamma values and thus and increased G gamma to A gamma ratio (Blood)] was present. No indication has yet been obtained explaining the elevation in both G gamma and A gamma chains; haplotyping showed that the chromosome carrying this G gamma A gamma(delta beta)+ determinant is unusual among the Chinese population.