A study was conducted on 115 full-term newborn infants with fetal-maternal ABO or Rh incompatibility submitted to exchange transfusion (EXT) due to hyperbilirubinemia. Donor blood was preserved in sodium citrate-sodium phosphate-dextrose-adenine (CPDA-1) and stored for a maximum of 48 hours. The volume of blood exchange was equivalent to two blood volumes of the infant and the procedure took approximately two hours. The following results were obtained with respect to bilirubins: 1) EXT let to a 44.03% reduction in indirect bilirubin in the ABO group and to a 43.40% reduction in the Rh group, thus demonstrating the efficacy of this procedure. 2) EXT was indicated earlier and in the presence of lower indirect bilirubin levels in the Rh group, which was also the group which required more frequent repetition of EXT (44.40% as opposed to 17.10% for the Rh group. 3) In both the ABO and Rh groups, the indirect bilirubin value that most closely approached the level for EXT indication was that obtained 3 hours post-EXT (least significant percent difference).