A major cause of morbidity and mortality in thalassemic patients is infections, assumed to be the result of immunological changes. In this study immune functions of peripheral blood lymphocytes have been studied in 38 beta -thalassemia major, 12 beta -thalassemia trait, and 17 healthy children. Results show decrease in CD4(+)/CD8(+) ratios in the beta -thalassemia major group and no difference according to absolute T-lymphocyte numbers and activated T-cell numbers. These results do not correlate with the tendency to infection. No significant difference was found in humoral immunity. The study of other factors in thalassemia is needed to detect those who are more susceptible to infections.