Three cases of autoimmune hemolytic anemia in infants are described. This disease is very rare in the first few months of life. One case (No. 3) was complicated with a rare hemoglobinopathy, which may have been coincidental. Corticosteroid treatment in larges doses was partially and temporarily effective in controlling the disease. Immunosuppressive therapy (azathioprine = Imuran, 2-5 mg./Kg./day) produced a complete cure in Case 1 and allowed a marked decrease in steroid doses in the other two cases. Most probably, a vicious circle of autoimmunity was broken by this drug. Failure to gain weight on steroids was more than compensated for by the clear-cut "catch-up growth" in Case 1, even though Imuran was being given. Indications regarding precautions and dosage of azathioprine are stated. The exact mode of action of these drugs is discussed in an attempt to explain the nature of immunosuppression.