SUMMARY C3, factor B, and x-l-antitrypsin were determined in newborn infants with septicaemia and sclerema, associated with suspected infections, ABO or Rh incompatibility, and hyperbilirubinaemia of unknown origin, during and after treatment with exchange transfusion. Activation products from C3 and factor B, the clearance of the transfused C3, and its synthesis by the recipient were determined also. Infected newborn infants had low levels of C3 and factor B, but a normal amount of x-1-antitrypsin. Exchange transfusion lowered the level of x-l-antitrypsin and briefly corrected the low level of C3 and factor B. Activation products were formed only exceptionally. Blood samples were obtained from the donors shortly before the transfusion, and from the patient at the beginning, at one-third or one-half, at two-thirds of the transfusion volume, at the end of the transfusion, and at 1, 3, 6, and 12 hours after it. Clotting was allowed to proceed at 40C and aliquots of serum were immediately frozen at -700C Samples of 0 5 ml blood were obtained from the. unbilical artery or from a heel prick.Quantitative determinations and certain other electrophoretic studies were run on an LKB multiphor system at 40C in the room (LKB-Produkter AB S-161-25 Bromma 1. Sweden). Plates were cooled at I OC by a Haake thermostat during the run (Haake Inc., Saddle Brook, NJ 07662 USA). Current was sLipplied by an LKB 2103 power supply. Alpha-lantitrypsin concentrations were measured by radial immunodiffusion2 using a commercial specific antiserum (Atlantic Antibody Corporation, Westbrook, Maine, USA). A reference serum was provided by Behring and Co (3550 Marburg (Lahn) Germany). C3 level was determined by electroimmunodiffusion,3 using a specific antibody in 1 % agarose in 0 05 mol/l veronal and 0 009 mol/l EDTA, pH 8-6 buffer. A pool of 12 fresh human sera, frozen in aliquots at -700C, was uised as a reference standard. 782 on 11 May 2018 by guest. Protected by copyright.