Proton and 13C nuclear magnetic resonance measurements indicate that uracil derivatives dissolved in chloroform bind to glycine and phenylalanine tripeptide derivatives through pairs of hydrogen bonds. The N(3)--H and C(4)=0 groups of the uracil ring appear to interact with the C=0 and N--H groups, respectively, of individual amino acid residues, suggesting a fundamental complementarity between uracil and the peptide backbone. The binding occurs in the same concentration range as the hydrogen bonding between derivatives of adenine and uracil under comparable conditions.