We investigated the incidence, clinical and immunological characteristics of human immuno-deficiency virus (HIV) infection in a group of multi-transfused patients with thalassaemia major who were exposed to transfusion-associated HIV infection. Seropositivity to HIV by Western blot and immunofluorescence analysis was detected in 26 out of 590 patients. At a follow up 21-40 months later, none of these seropositive patients had developed acquired immuno-deficiency syndrome (AIDS), and six manifested the AIDS related complex (ARC). ARC was unusually mild and consisted of moderate laterocervical and submandibular lymph node enlargement associated with hypergammaglobulinaemia and a reduced CD4/CD8 ratio resulting from the decreased number of CD4 lymphocytes. These findings suggest that multi-transfused patients with thalassaemia major are relatively resistant to the development of severe manifestations of HIV infection, presumably because their immune status is relatively better preserved than that of other infected populations. Longer follow up is, however, necessary to determine whether the incidence of AIDS will be lower in this population or whether overt AIDS merely takes longer to develop.