Coinheritance of alpha-thalassemia and hemoglobin E (Hb E) is prevalent in Thailand, where the gene frequencies of thalassemia and hemoglobinopathies are high. Hb E carriers with, concomitant inheritance of alpha-thalassemia 1 are known to have a lower level of Hb E. In this study, we reviewed the Hb E levels in Hb E carriers, who either had or did not have Southeast Asian (SEA)-type alpha-thalassemia, in order to seek a Hb E level that may be used as a predictor for concomitant alpha-thalassemia carrier status. The Hb E levels as measured by microcolumn chromatography in 844 Hb E carriers detected during a prenatal screening program for severe thalassemia at Chiang Mai University Hospital were reviewed. Hb E levels ranged from 12.3-35.0% (23.3 +/- 3.1%) in 751 Hb E carriers without SEA-type alpha-thalassemia and from 11.6-32.0% (17.0 +/- 3.7%) in 93 concomitant Hb E and SEA-type alpha-thalassemia carriers. The difference was significant (p < 0.01). However, the absence of SEA-type alpha-thalassemia could not be predicted by the higher Hb E level alone, as 3% of double heterozygotes demonstrated a level of more than 25%. Our study confirms a lower Hb E level in double heterozygotes with Hb E and SEA-type alpha-thalassemia. Nevertheless, the difference does not provide sufficient discriminatory power for the reliable exclusion of alpha-thalassemia status.