The biologically important compound hydrated disodium adenosine 5'-triphosphate (ATP) was studied focusing on the Na-23 nucleus (spin quantum number I = 3/2) as probe in various solid-state NMR techniques including magic-angle spinning (MAS), cross-polarization MAS (CPMAS) and multi-quantum MAS (MQMAS) at 4.7 and 9.4 T. MQMAS experiments enabled the resolution of all the four crystallographically different Na-23 sites in the unit cell in the MQMAS spectrum at 4.7 T, but not at 9.4 T. The four sites were successfully assigned and the principal elements of the quadrupolar tensors and isotropic chemical shifts of the Na-23 nuclei at each lattice site determined by analyzing and computer simulating the above experimental spectra.