In kwashiorkor, there is less endogenous proteolysis in response to acute infection than in a well-nourished state. Thus the amino acid composition of dietary protein may be more important in facilitating the acute phase response in kwashiorkor. This study tested the hypothesis that during the treatment of kwashiorkor with infection, there is a lower rate of urea appearance when the dietary intake of amino acids more closely resembles the amino acid composition of acute phase proteins. Thirty children in Malawi with kwashiorkor and acute infection were fed isoenergetic, isonitrogenous meals containing either egg white-tryptophan or milk as a protein source. After 24 h, the rates of urea appearance and whole-body protein breakdown and synthesis were measured with the use of 1-13C-leucine and 15N2-urea tracers. Plasma concentrations of seven acute phase proteins, interleukin 6 and tumor necrosis factor-alpha were measured on admission, and at 24 and 48 h. The 16 children who received egg white-tryptophan had lower rates of urea appearance than those who received milk [57+/-30 vs. 87+/-36 micromol/(kg x h), mean +/- SD, P<0.02]. No significant differences were found in the rates of whole-body protein turnover or in the concentration of any of the acute phase proteins or cytokines. The concentration of interleukin 6 was consistent with an appropriate proinflammatory response and correlated directly with the concentrations of C-reactive protein (r = 0.67, P<0.01) and alpha1-antitrypsin (r = 0.40, P<0.05). The findings suggest that egg white-tryptophan is associated with less amino acid oxidation in kwashiorkor and acute infection than is milk.