Albumin-kinetic studies were performed in nine uraemic patients without oedema on chronic haemodialysis and in seven normal controls in order to determine microvascular leakiness and thereby, during steady state, lymph drainage of albumin. Transvascular escape rate of albumin [TERalb i.e. the fraction of intravascular mass (IVMalb) passing into, or returning from, the extravascular space per unit time] and the distribution ratio (DRalb) between IVMalb and total albumin mass were determined from intravenously injected radioiodinated serum albumin. Before haemodialysis, TERalb was significantly elevated (mean 9 X 6% IVMalb h-1, range 5 X 9-14) as compared to the value 15 h after haemodialysis (mean 7 X 3, range 5 X 2-11, P less than 0 X 02) and to controls (mean 5 X 9, range 4 X 3-7 X 4, P less than 0 X 01). Average DRalb (mean 0 X 54, range 0 X 44-0 X 69) was clearly elevated in patients with respect to controls (mean 0 X 44, range 0 X 42-0 X 48, P less than 0 X 01), and the extravascular mass of albumin was significantly decreased (mean 27 X 9 mumol kg-1, range 14.1 - 41.2 v. mean 35.9, range 27.1 - 43.8, P less than 0.05). We interpret the results as to indicate increased transvascular filtration of albumin in microcirculatory beds with permeable capillaries (splanchnic organs), in between the haemodialysis treatment, and filtration of protein-poor fluid in areas with 'tight' capillaries (skeletal muscle, cutis) resulting in interstitial space protein depletion here. As the patients were considered to be in steady state during the measurements, the increased TERalb indicates increased lymph flux of albumin. The interstitial space protein 'wash-down' and increased lymph drainage probably serve as oedema prevention.