In order to determine the extent to which the concentration of albumin in plasma is maintained at the expense of the extravascular pool during protein-energy malnutrition, the rates of exchange between albumin in plasma (1A) and the extravascular pool (EA) and consequently the distribution of albumin between intravascular and extravascular pools (expressed as EA:IA) were measured in protein-energy-depleted and control rabbits. The fractional rates of synthesis (FSR) and catabolism (FCR), the concentration of albumin and the plasma volume (PV) were also measured. In animals in which protein-energy intake was reduced by 58% the concentration of albumin in plasma remained unchanged, whereas FCR decreased by 38 % and FSR by 30 YO. No significant changes in EA: IA or PV were found. We conclude that albumin concentration during proteirrenergy depletion is not maintained at the expense of extravascular albumin, but by parallel changes in the rates of catabolism and synthesis.