In Thailand, two types of high Hb A2-beta-thalassemia genes: beta0-thalassemia (beta0-thal) or classical beta-thalassemia and beta+-thalassemia (beta+-thal) or mild beta-thalassemia exist. This study presents hematologic data and globin chain synthesis in peripheral blood of the genuine beta+-thal heterozygotes in comparison with those of the beta0-thal heterozygotes. Thirty individuals of Thai and Chinese extraction with the beta+-thal heterozygosity were hematologically examined. The hematologic means of hemoglobin concentration, MCV, MCH, MCHC, Hb A2 and alkali denaturation hemoglobin of the beta+-thal traits were, 11.7 g%, 67.8 mu3, 21.5 gammagamma, 32.1%, 4.94% and 1.20% respectively. These were not statistically different from those of the beta0-thal traits of our previous study(1). The globin chain synthesis in reticulocytes were performed by incorporation of 3H-Leucine for 3 hours. The mean of total radioactivity alpha/beta ratio in 11 normal controls was 1.07 +/- SD 0.03. The mean of alpha/beta ratio in 9 beta+-thal traits was 2.03 +/- SD 0.10 which was significantly different from that in 7 beta0-thal traits of 2.28 +/- SD 0.07. Our globin chain synthesis thus appears to be helpful of discriminating the beta+-thal trait from the beta0-thal trait.