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Double cross-polarization (1)(DCP) NMR is an extension of cross polarization (2) to systems containing three different spin-l/2 nuclei, in particular systems containing ‘H, 13C, and “N. The experiment involves first a transfer of polarization from abundant protons to either carbons or nitrogens, followed by removal of the proton rf field together with a spin-lock contact of carbons and nitrogens. Either 13C or 15N spins can then be observed, resulting in spectra of high sensitivity which contain information about carbon-nitrogen dipolar coupling. The technique has been used for the detection of labeled 13C-“N chemical bonds in complicated intact biological systems (3, 4). To detect labeled CN bonds quantitatively, the relaxation parameters controlling the 13C-15N transfer must be measured accurately. In the past, this has been done with extensive use of multiple-labeled model compounds (4). Recently, we have …