Spin dynamic simulation techniques were used to study the influence of static-zero field splitting (zfs) interactions on the NMR paramagnetic relaxation enhancement (PRE) produced by the spin-5/2 complex Mn(II) -TSPP (TSPP = tetrakis(sulfonatophenyl)porphyrinate). The NMR-PRE produced by this complex, recently reported by Bryant ct al. (Inorg. Chem. 1999, 38, 1002), has a magnitude and magnetic field dependence that differ markedly from the predictions of the classical Zeeman-limit theory of Solomon, Bloembergen, and Morgan. We show that this failure results from the influence of the static zfs interaction. Inclusion of a zfs coupling of magnitude D = 0.3 cm(-1) in the electron spin Hamiltonian, in conjunction with a realistic description of the effects of Brownian reorientation on the electron spin motion, produced an accurate fit of the experimental T-1 magnetic field dispersion profile. It is shown that the observed dispersion in the NMR-PRE field dispersion profile results from a change in the axis of spatial quantization from a molecule-fixed to a laboratory-fixed axis that occurs as, with increasing Zeeman-field strength, the zero-order electron spin Hamiltonian changes from the zfs Hamiltonian to the electronic Zeeman Hamiltonian. The results demonstrate the profound importance of the static zfs interaction in analyses of the NMR paramagnetic relaxalion enhancement for S greater than or equal to 1 ions, even in systems where the static zfs is very small (\ D \ < 0.1 cm(-1)). They also illustrate the utility of NMR relaxation data for measuring static zfs couplings.