Two cases of Thai subjects with abnormal hemoglobin (Hb) detected on a cellulose acetate electrophoresis are reported. Both abnormal Hb S migrated between Hb A2 and Hb A at pH 8.6. In the first case, a 23-yr-old Thai male, hematologic analysis gave the following data: Hb 15.0 g/dl, Hct 43 %, MCV 83 fl, MCH 29 pg, MCHC 35 g/dl and RDW 14.2%. The second case, a 26-yr-old Thai male, had Hb 16.3 g/dl, Hct 48 %, MCV 88 fl, MCH 30 pg, MCHC 34 g/dl and RDW 12.5%. Analysis using an automated HPLC Hb Analyzer identified abnormal Hb peaks with 39.2% at the S-window in the former and a 33.1% at the D-window in the latter. Since the mobility of these two abnormal Hbs are similar to that of the Hb Tak, another common abnormal Hb found in Thailand, identification of the β^Tak mutation using an allele specific PCR was carried out. With this analysis, the β^Tak mutation was detected in the latter, indicating that he was a Hb Tak heterozygote, but not in the former case. Further DNA sequence analysis of the  β-globin gene of the first case identified a GAG (Glu) to GTG(Val) mutation at codon 6 which is characteristic of the Hb S. Screening for Hb S using the Sickling test was also positive in this case. β -globin gene haplotype analysis demonstrated the heterozygosity of the two different haplotypes in this subject. Though the β^S associated haplotype could not be clearly defined in this Thai subject with Hb S carrier, it was presumed that the Thai β^S gene had the same origin as that of Indians due to similarities at some polymorphic sites. A simple DNA assay based on allele specific PCR for rapid diagnosis of the Hb S is also described.