A considerable proportion of the nitrogen of beer wort is known to exist in the form of peptides; it is therefore important to know what value this class of compounds has as a source of nitrogen for yeast. The following paper reports the results of an examination of the nutrient proper ties of some simple peptides in comparison with the related amino acids. It is shown that dipeptides tend to be perceptibly less efficient nutrients than free amino acids, and it also seems probable that their nutrient efficiency rapidly diminishes as the number of amino acid residues they contain is increased. As regards the mechanism of their assimilation, they appear first to be hydrolyzed by yeast into their component amino adds which are then deaminated by the Ehrlich mechanism.