A sensitive triple resonance NMR experiment Is presented for the measurement of the protein backbone dihedral angle psi based on cross-correlated spin relaxation between C-13(alpha)-H-1(alpha) and N-15-(HN)-H-1 dipolar interactions in N-15,C-13-labeled proteins. In general, as many as four yi values can be consistent with a single cross-correlation rate. However, in many cases, the ambiguity can be significantly reduced (for example, from four to two) when a combination of cross-correlation relaxation rates are employed. This is illustrated by considering rates derived from (Calpha-1Halpha)-C-13/N-15-(HN)-H-1 dipolar and from C-13(alpha)-H-1(alpha) dipolar/carbonyl chemical shift anisotropy relaxation mechanisms for the proteins ubiquitin and CheY. Using a database of psi values obtained from high-resolution X-ray structures, it is shown that for values in the range -50 degrees less than or equal to psi less than or equal to 40 degrees a single psi can be obtained to high probability.