As determined in rabbits, the in vivo plasma survival, i.e. half-life (t½), of albumin produced by the cold-ethanol procedure did not differ significantly from that of native albumin (p>0.5). Plasma survivals of reprocessed and heat-ethanol produced albumins were significantly less than that of the native protein (0.02 < p < 0.05). Chemicallymodified albumin had a considerably reduced t½ (p< 0.001) and was the only albumin shown to be antigenically different from the native protein. Variations in t½s of albumin preparations could not be attributed to differences in their polymer contents.