1. To examine whether insulin resistance in uraemia extends to amino acid metabolism, the effect of physiological hyperinsulinaemia on plasma amino acid concentrations was studied in 17 chronically uraemic and 28 healthy subjects by using the euglycaemic insulin clamp technique. 2. In six uraemic and seven control subjects, splanchnic and leg exchange of amino acids was quantified with hepatic and femoral venous catheterization, and in five uraemic and eight control subjects intracellular free amino acid concentrations were determined in muscle tissue obtained by needle biopsy. 3. In response to hyperinsulinaemia the plasma concentrations of all amino acids except alanine decreased by 10-50% in both uraemic and control subjects. Splanchnic alanine uptake declined by 20% and leg amino acid release tended to decrease in both groups. 4. The intracellular levels of all measured amino acids except alanine fell significantly and to a similar extent in uraemic and control subjects. 5. These results indicate that insulin-mediated alterations in regional amino acid exchange and in plasma and intracellular amino acid concentrations are similar in uraemic and control subjects. 6. It is concluded that tissue insensitivity to insulin in uraemia does not extend to uptake or release of amino acids and that resistance to insulin can be selective in its effect on different metabolic functions.