A significantly lower incidence of DDS, hypotension, and impending shock was found during and after hemofiltration as compared with conventional hemodialysis. Hemofiltration, in contrast to hemodialysis, showed less decrease of circulating plasma volume, mild change in plasma osmolality without red cell swelling, better compensation of acidosis despite less uptake of acetate, more stable PCO2 during the procedure, less paradoxical acidosis in cerebrospinal fluid, and a lower urea concentration gradient between cerebrospinal fluid and plasma. These phenomena might be explained by better mass transfer between compartments bithin the body during hemofiltration. Mass transfer from the intracellular as well as the extracellular space to circulating plasma occurred more rapidly and smoothly during HF than during HD. HF is preferable to HD in patients with severe cardiovascular complications such as hypertension, as well as hypotension and cardiac failure, and in those subject to DDS during HD. Accordingly, hemofiltration therapy promises patients more comfortable and more stable treatment of chronic uremia.