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Sequencing amino acid units in peptides with molecular weights of 1000-2300 Da can be difhcult. The use of NOE-based experiments, for example, is frequently hampered by unfavorable rotational correlation times in this molecular weight range. The resulting lack of NOES between adjacent amino acid residues, coupled with the presence of nonsequential NOES in peptides due to intramolecularly hydrogenbonded amide groups, can sometimes lead to incorrect sequence assignments. Moreover, the use of long-range ‘H-13C or ‘H-j5N correlation experiments to sequence amino acid units through the amide carbonyls and nitrogens is often restricted by the combination of small coupling constants and short T2’s. The difficulties in using homonuclear and heteronuclear ‘H NMR techniques to sequence amino acids in smafl peptides have prompted us to devise a procedure on carbon-detected 13C-15N correlation spectroscopy. This experiment is of course difficult to perform at the natural abundance levels of r3C and “N. If the peptide is enriched with r5N to about 1570, however, sequencing can be achieved in a onedimensional experiment by correlating decoupled 13C signals in the carbony and a-methine regions with selectively irradiated 15N resonances. This approach has previously described by Llinas et al. (I). At 15N enrichment levels as low as 30-4096, two-dimensional correlation experiments become possible and in this report we describe our progress in examining the different approaches to this methodology. The logical first choice of experiments is an extension of the classical chemicalshift correlation (2). The basic pulse sequence is of the type