The synthetic peptides Gly5-epsilon-Ahx and L-Ala3-epsilon-Ahx, with structural similarity to the interpeptide bridge peptides of staphylococci or micrococci, respectively, were convalently linked to human serum albumin via their carboxylgroups. Antisera to these synthetic peptidyl-protein antigens contained fairly high amounts of antibodies with specificity to the N-terminal parts of the peptide chains attached to the carrier proteins. Antisera to (Gly5-epsilon-Ahx)20-albumin gave, without exception, strong precipitin reactions in latex-agglutination with staphylococcal peptido-glycans. The antisera completely failed, however, in any reaction with peptidoglycans of micrococci or other bacteria which did not have these oligo-glycine peptides typical for staphylococci. On the contrary, antisera to (l-Ala3-epsilon-Ahx)22-albumin strongly precipitated micrococcalpeptidoglycans with oligo-L-alanine interpeptide bridges (e.g. Micrococcus varians. Micrococcus roseus), but showed no significant reaction with peptidoglycans of staphylococci or other bacteria lacking oligo-L-alanine interpeptide bridges.