A technique is proposed which simplifies the study of spin-lattice relaxation in multilevel nuclear spin systems. The introduction of non-participating \"spy\" nuclei, which interact with the nuclei under investigation through scalar or dipolar coupling, makes it possible to monitor relaxation due to dipolar, quadrupolar and random field interactions. Two-dimensional Fourier transform spectroscopy was used to provide a direct visualization of the relaxation matrix. [on SciFinder (R)]