Nitrogen balance was studied in 4 patients with uremia during treatment with a protein-reduced diet (20 g) supplemented with either essential amino acids and histidine or a mixture of keto analogues of five of the essential amino acids and essential amino acids. 3 patients completed the study. Nitrogen balance was negative on the diet only and was improved with both forms of supplementation. However, supplementation with the keto acids did not offer any advantage over the conventional essential amino acid supplementation. 1 patient developed serious hypercalcemia during treatment with the keto acid supplementation.