Earlier studies have shown increased oxidation of the branched-chain amino acids (BCAA), valine, isoleucine and leucine, in experimental acidosis and low levels of valine in the muscle of acidotic HD patients. Using HPLC, free amino acids in plasma and muscle were studied before and after correction of acidosis in 9 HD patients over 6 months by dialysis with a high bicarbonate solution. The predialysis standard bicarbonate concentration in blood increased from 20.6 +/- 1.3 mmol/l (mean +/- SD) before correction of acidosis to 25.9 +/- 1.8 mmol/l after correction. Correction of acidosis resulted in a significant increase in the i.c. concentrations of valine, isoleucine and leucine by 48%, 28% and 32%, as well as for the sum of BCAA and EAA, from a level lower than controls. The intra- and extracellular gradient increased for several amino acids and for the sum of EAA and BCAA, suggesting an increased influx or reduced efflux of amino acids across the cell membrane. Anthropometric data and the levels of S-albumin and transferrin did not change after correction of acidosis. The increases in the i.c. concentrations of BCAA after correction of acidosis suggest that the catabolism of these amino acids had been reduced. The effects of correction of acidosis on the concentrations of essential amino acids could be beneficial since low concentrations in muscle may reduce protein synthesis.