The nuclear Overhauser effect, which mon itors the transfer of nonequil ibrium magnetization of a spin to its neighbors via mutual dipolar relaxation, has in recent years become a powerful tool for structure elucidation of biomolecules in solution. There are several oneand two-dimensional experiments used for mon itoring this effect. In the one-dimensional driven nuclear Overhauser effect experiment the magnetization of a spin is continuously saturated and the transfer to the other spins takes place in the presence of the saturating radio-frequency field (I). A difference spectrum reveals the relaxation transfer to the other spins. The exact amount of transfer is a function of many parameters, including the distance between the spins. Careful analysis of this data is needed before mean ingful distance information can be obtained and therefore the driven NOE data are often interpreted only qualitatively. In the transient NOE experiment, first proposed by Solomon (2,3), the magnetization of a spin is selectively inverted, and the relaxation transfer to other spins is mon itored in the absence of the RF field. The magnetization transport follows simple rate equations, with a welldefined initial condition, and often the initial rate of transfer can be directly related to the inverse sixth power of the internuclear distance. The magn itude of transfer in a transient NOE experiment is generally lower than the driven NOE experiment and therefore the signal-to-noise ratio in the difference spectrum is poorer. The two-dimensional NOE experiment (NOESY) has largely replaced the above experiments, by yielding the relaxation-coupling information for all the spins in a single experiment. The NOESY experiment uses the sequence 90”-t,-90”-7,-90”-t,, in which the relaxation transfer takes place during 7,. The rate equations governing relaxation transfer in a NOESY experiment are identical to the transient NOE experiment including the initial condition. It has been shown that each cross section in a NOESY experiment is identical to a transient NOE experiment with the selective inversion of the diagonal peak (4, 5). When there are J couplings present, selective inversion is to be carefully defined. It has been shown recently (6, 7) that a NOESY experiment with a small second pulse [90”-t,-a”-7,-90”-t, with small a! (in linear approximation)] is equivalent to a transient experiment, such that a cross section parallel to w2 at a frequency w, is equivalent to a transient NOE experiment in which the transition at frequency w, is selectively inverted. It has been further shown that this is true whether the J coupling