Summary. The effect of iron deficiency anaemia (IDA) on CD71 expression by peripheral blood lymphocytes was studied in 43 children with iron deficiency anaemia. 18 healthy age-matched children were selected as the control group. 11 children with b-thalassaemia trait were also studied. Lymphocytes bearing CD71 were enumerated by flow cytometric analysis of peripheral blood. At diagnosis, CD71 þ peripheral lymphocytes (mean Ϯ SE) was 5·90 Ϯ 0·76% in patients with IDA and 12·60 Ϯ 0·98% in healthy controls (P ¼ 0·000). In b-thalassaemia trait patients the peripheral blood CD71 þ lymphocytes were 7·80 Ϯ 1·20%. In IDA patients there was a statistically significant correlation between the levels of CD71 þ peripheral lymphocytes and haemoglobin value (P ¼ 0·000). In 19 patients studied at days 0 and 30 of oral iron therapy, the number of peripheral blood CD71 þ lymphocytes was shown to be increased from 5·90 Ϯ 0·76% to 12·11 Ϯ 1·21%. In severe IDA presence of a limited number of CD71 þ peripheral blood lymphocytes indicated that severe IDA should be borne in mind when considering conditions responsible for the suppression of lymphocyte proliferation.