“…The only accurate and practical method of recognizing a-thalassaemia trait is the demonstration of increased amount of Hb Bart's at birth. We have found that the amounts of Hb Bart's at birth are positively correlated with the severity of a-thalassaemia (Pootrakul et al, 1967a, b;Pootrakul et al, 1970; Na-Nakorn & Wasi, 1970); the concentrations of Hb Bart's in the cord blood of roo, 25, 5 and I-2% respectively represent a-thal, homozygosity, a-thalJa-thal, , a-thal, trait and a-thal, trait. cord blood data fiom Thailand (Pootrakul et d, 1970; Na-Nakorn & Wasi, 1970) and segregation of the amounts of Hb Bart's in 3 I newborn offspring of Hb H patients (Na-Nakorn et al, 1969) support the hypothesis of two a-thalassaemia alleles at a single locus.…”