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Immunological abnormalities have been observed in many haemophiliacs receiving clotting factor concentrates. To determine whether similar changes also occur after repeated blood transfusions we estimated T cell subsets and cutaneous delayed hypersensitivity (CDH) in 50 multitransfused children with β-thalassemia major (β-TM). All patients were also tested for anti-HTLV-III/LAV antibodies. A diminished percentage of T lymphocytes (E-rosettes, T3+), and T4+ cells and a low T4/T8 ratio was found in patients as compared to age and sex matched controls (P <0.001). Negative CDH tests to specific antigens (Multi-test) were also found in a significantly larger proportion of β-TM children (P <0.01). Antibodies against HTLV-III/LAV were negative in all patients. Decreased T4/T8 ratio in β-TM children was primarily due to a reduction of T4+ cells and was inversely correlated to the patients" age, number of units of transfused blood (P <0.05) and especially to ferritin serum levels and annual iron balance (P <0.001). These findings indicate that immunological abnormalities in β-TM patients appear to be acquired, transfusion-associated and related to iron load which depends on the appropriate chelation therapy. [ABSTRACT FROM AUTHOR]