The interactions of cis-and trans-glyoxal and glycine as a prototype of a carboxylic end of a protein, and the interaction of glyoxal and N-methylacetamide as a prototype of a peptide bond are discussed. Part of their potential-energy surface is given as obtained by the CNDO/2 approximation. It is observed that both glyoxal isomers form different complexes with glycine; with Nmethylacetamidc they give the same molecular complex. The results suggest more experimental search for derivatives of both glyoxal isomers in normal cells.