The purpose of the proposed research is to determine the effectiveness of exchange transfusion in the management of the small and/or sick premature infant. The study is designed to examine whether any potential benefits are derived from facilitation of oxygen release produced by the substitution of low affinity adult hemoglobin for high affinity fetal hemoglobin or whether the benefits are produced by alterations in the coagulation mechanism. The exchanged and non-exchanged infants will also be utilized to examine the relationship of the postnatal fall in hemoglobin and the sequential changes in the affinity of hemoglobin for oxygen to the resumption of accelerated erythropoiesis and erythropoietin production during the first 10 to 16 weeks of life.