A Thai family with a complex thalassemia syndrome caused by alpha- and beta-globin defects is described. The proband was a 14-year-old boy who had chronic hypochromic microcytic anemia. Hemoglobin (Hb) and DNA analyses demonstrated that he carried Hb Beijing [alpha16(A14)Lys-->Asn], Hb E [beta26(B8)Glu-->Lys] and alpha-thalassemia-1 (alpha-thal-1). Interaction of the alphaBeijing with the betaE globin chains in the proband leads to a new Hb variant, namely Hb E Beijing with different characteristics to both Hb E and Hb Beijing. Family studies showed that his father carried Hb Beijing and Hb E, whereas his mother was a simple alpha-thal-1 carrier. The genotype-phenotype relationship observed in this Thai family with complex hemoglobinopathies is presented and a simple DNA assay based on allele specific polymerase chain reaction (ASPCR) for detection of Hb Beijing is described.