The NMR paramagnetic relaxation enhancement (NMR-PRE) induced by transition metal ions with electron spin S = 1 is strongly influenced by zero-field splitting (ZFS) interactions when the ZFS Hamiltonian is comparable or greater in magnitude than the electronic Zeeman Hamiltonian (H-ZFS greater than or equal to H-Zeem) In the vicinity of the ZFS limit (H-ZFS much greater than H-Zeem), the spatial quantization of the electron spin motion is oriented along the molecule-fixed principal axes of the ZFS tensor. In this situation, the NMR-PRE, corrected to constant electron-nuclear interspin distance, has been predicted to be a function of the orientation of the electron-nuclear interspin vector with respect to the principal axes of the molecular frame. This prediction was tested experimentally and confirmed for S = 3/2 using the complex, Co-II(acac)(2)(H2O)(2), for which the ZFS-limit axial/equatorial T-1 ratio, rho = 2.7 +/- 0.4, is substantially greater than the Zeeman limit value of unity. A second theoretical prediction has been tested concerning characteristic differences in the effect of ZFS rhombicity on the magnetic field profile of the NMR-PRE produced by integer and half-integer spins. For S = 1, the ZFS-limit NMR-PRE is profoundly depressed due to the effects of the orthorhombic terms of the ZFS tensor, a phenomenon which results physically from the splitting of the \+/-1] non-Kramers doublet by ZFS rhombicity and consequent alterations in the spin eigenfunctions. This depression is reversed by the application of a Zeeman field when the Zeeman energy exceeds the \+/-1] doublet splitting produced by ZFS rhombicity. Thus, the NMR-PRE of orthorhombic S = 1 Ni(II) complexes exhibits a characteristic dispersive feature in which the NMR relaxation efficiency increases several-fold between about 0.2 and 10 T. For half-integer spins, this phenomenon is expected not to be present because the Kramers doublets remain unsplit by ZFS interactions of any magnitude or symmetry. This prediction was tested and confirmed through measurements of the magnetic field dependence of the NMR-PRE produced by the S = 3/2 complex, Co-II(acac)(2)(H2O)(2), the NMR-PRE behavior of which differed qualitatively from that of the analogous S = 1 complex, Ni-II(acac)(2)(H2O)(2), as well as from other previously studied S = 1 model compounds.