The haematological data are presented in 312 individuals of Thai or Chinese extraction with the high A2 p-thalassaemia trait. The mean haemoglobin concentrations were 12.1 g x among males and 10.8 g"/;: among fcmalcs; 54% of thc subjccts wcre not anacmic and all wcrc asyniptomatic. Low MCV, MCH and MCHC values were found in 67%, 81 % aiid 6 "/, rcspcctively; erythrocytosis was detected in 34 %. Variable hypochromia and microcytosis were usually present, but