The unusual occurrence of both β°-thalassemia and autoimmune hemolytic anemia (AIHA) in a 28-month-old child is reported to illustrate special diagnostic and therapeutic studies. The diagnosis of β°-thalassemia was established by clinical, family and globin synthesis studies. The diagnosis of AIHA was confirmed by the shortened survival of transfused autologous and homologous red blood cells and by positive direct antiglobulin tests. During treatment of the AIHA with corticosteroids and various immunosuppressive drugs, globin synthesis studies were performed to evaluate the coincidental effects on γ/α-globin chain synthetic ratios. A 50% increase in the γ/αsynthetic ratio during cyclo-phosphamide treatment suggests that further studies of the possible benefits of cytotoxic drug therapy in β-tlassemia may be indicated.