Aspects of the humoral and cellular immune response have been studied in polytransfused patients with beta-thalassaemia major. Serum immunoglobulins (G, A, M) levels were significantly higher than in controls; reduced C4 serum level and high incidence of circulating immune complexes and anti-nuclear autoantibodies were found in the majority of patients. Marked increases were also observed in absolute and relative numbers of lymphocytes and their subpopulations. Such results suggested that the allogenic stimulation, by frequent transfusion, is the mainly responsible of the immunological alterations observed in these patients.