Plasma amino acids were measured by ion-exchange chromatography in 10 children on regular hemodialysis for renal failure before and after a 6 month period on an oral supplement of 8 essential amino acids. The supplement constituted 14.7 +/- 9.7 (1 SD) of the protein intake, the proportion varying inversely with protein intake, and mean energy and protein intakes which were normal for body size did not change significantly during the study. Before supplementation there were significant reductions compared to normal in the concentration of valine, leucine, isoleucine, lysine, histidine, tyrosine and serine, and elevations in glycine, proline and the methylhistidines. After supplementation methionine levels were abnormally high, isoleucine levels were in the lower range of normal and otherwise there were no significant changes. These modest changes suggest that supplemental essential amino acids in uremic children on adequate energy and protein intakes may not only be superfluour but may induce new imbalances which may themselves be harmful.