Summary The utilization of glutaminylglycine and glycylglutamine by Lactobacillus arabinosus was compared with that of glutamine and glutamic acid. The growth response to these peptides in its dependence upon concentration or upon time as well as the action of these peptides toward glutamic acid antimetabolites was indistinguishable from that of glutamine. It is therefore suggested that the peptides serve as a source of free glutamine liberated by enzymatic action. In contrast to the behavior of the glutamine peptides, asparaginyl-glycine and glycylasparagine are significantly better utilized than asparagine by both Leconostoc mesenteroides and L. arabinosus. Their utilization approximates that of aspartic acid. The significance of this finding is discussed.