Two unrelated cases of compound heterozygosity for Hb Hekinan [alpha27(B8)Glu-->Asp (alpha1) and alpha-thalassemia have been found in Thailand. Mutations were established at protein level by peptide mapping and at the DNA level by direct sequence analysis. Proband S.S. had genotype - -SEA/alpha2(A)alpha1Hekinan, betaA/betaE, while an unrelated proband, S.J., is the first case described with the genotype - -SEA/alpha2(A)alpha1Hekinan, betaA/betaA. Both alpha1Hekinan mutations were located in the alpha1 locus. Hb Hekinan could not be accurately estimated by HPLC, since it was poorly separated from Hb A. However IEF gave good separation of Hb Hekinan and Hb A, leading to estimates of Hb Hekinan (alpha Hekinan 2/beta A 2 and alpha Hekinan 2/beta E 2) level as 40-43% of total Hb.