We undertook a four year study of 128 thalassaemic patients who had undergone several transfusions, to determine the incidence of hepatitis B virus markers and the activities of transaminases in their sera each month. The results showed that the possibility of these patients contracting hepatitis B virus infection is still high, although on only one occasion was a transient antigenaemia found, indicating low viral replication. Furthermore, the probability of contact with hepatitis B virus increases with the number of transfusions and, therefore, with age. About 25% of these patients were positive for hepatitis B markers and 80% for other hepatitis markers including the case of cytomegalovirus hepatitis.