A study of serum β<sub>2</sub>-microglobulin and urinary β<sub>2</sub>-microglobulin in patients with liver and/or kidney disease was done to determine if such information is of diagnostic help. Serum concentrations and β<sub>2</sub>M/Cr clearance ratios are higher in patients with primary tubular disorders than in those with glomerular diseases, a finding unaltered by hepatic disease. These data suggest either an increased production or decreased tubular degradation of β<sub>2</sub>M, independent of the glomerular filtration rate (GFR), in primary tubular disorders. The marked increase in urinary β<sub>2</sub>-microglobulin that followed insertion of the peritoneal-jugular shunt is evidence that this procedure resulted in improvement of the GFR, in previously underperfused nephrons.