A Turkish family is described in which three children have a clinical picture similar to that of thalassemia major, with typical red cell morphology and indices, and with about 10% Hb Bart's but without measurable amounts of Hb H. Hematological evaluation of six members of this family that included in vitro hemoglobin synthesis suggests that beta-(or delta beta-) thalassemia, beta-silent thalassemia, and mild and severe alpha-thalassemia genes are present in different combinations. The data indicate that beta/alpha chain ratios in patients with more than one type of thalassemia should be evaluated in relationship to values obtained for several relatives even though some of the thalassemia determinants may be silent in the parents.