We describe hematologic and DNA characterization of hemoglobin (Hb) E homozygote with various forms of alpha-thalassemia in Thai individuals. Altogether, 131 unrelated adult subjects with Hb EE at routine Hb analysis were studied. Forty-two cases were found to carry alpha-thalassemia with ten different genotypes. These included 21 cases with alpha(+)-thalassemia heterozygote (-alpha(3.7)/alphaalpha), one case with alpha(+)-thalassemia heterozygote (-alpha(4.2)/alphaalpha), six cases with Hb Constant Spring heterozygote (alpha(CS)alpha/alphaalpha), four cases with homozygous alpha(+)-thalassemia (-alpha(3.7)/-alpha(3.7)), one case with homozygous alpha(+)-thalassemia (-alpha(4.2)/-alpha(4.2)), two cases with compound alpha(+)-thalassemia/Hb Constant Spring (-alpha(3.7)/alpha(CS)alpha), one case with compound alpha(+)-thalassemia/Hb Paksé (-alpha(3.7)/alpha(PS)alpha), four cases with alpha(0)-thalassemia heterozygote (--(SEA)/alphaalpha), and, unexpectedly, two cases with compound alpha(0)-thalassemia/alpha(+)-thalassemia [(--(SEA)/-alpha(3.7)) and (--(SEA)/-alpha(4.2))]. The hematological expression of these Hb E homozygotes with various forms of alpha-thalassemia was presented comparatively with those of the 89 cases of pure Hb E homozygotes. Overlapping levels of Hb E, Hb F, and other hematological parameters were observed which did not predict clinical severity, indicating a need for alpha-globin gene analysis for accurate diagnosis and improved genetic counseling.