Studies were conducted on the effects of feeding D-amino acids on growth rate and D-amino acid oxidase (DAAO) in chick kidney. The crystalline amino acid (AA) diet provided seven amino acids either in the L-form or the DL-form at two concentrations (DL- or .5 DL-AA diets) with all diets containing equal amounts of L-amino acids. Weight gains of chicks fed the DL-AA diet were consistently lower than those fed the L- or .5 DL-AA diet. Kidney DAAO activity was significantly higher in chicks fed either the DL-AA or .5 DL-AA diet as compared with the L-AA diet. Kidney DAAO activity was essentially the same in chicks fed the DL- and .5 DL-AA diets. Increasing the nonspecific nitrogen in the diet had no effect in alleviating growth depression of the DL-AA.