Summary of the results of time-course globin chain synthesis studies. Results are expressed as the ratio of the increase in specific activity of the β or β^E chain in the first hour to the increase in the second hour. The log₁₀ of the ratio is plotted. If SA increases linearly, the ratio is 1 (log₁₀ 0); as the hemoglobin becomes unstable and the SA increases less in the second hour, the ratio increases exponentially. (○) Incubation at 37°C, (◍) incubation at 39°C, (•) incubation at 41°C, (⊟) sample was also deficient for pyrimidine 5’ nucleotidase. E/beta thal, E/β thalassemia (includes bone marrow sample and unwashed, whole blood); EE, homozygous HbE; TI, thalassemia intermedia. The log(SAβ 1 hour/SAβ 2 hours) is 0 in HbE/β thalassemia at 37°C, but increases markedly at higher temperatures. This effect is not seen in β thalassemia intermedia.