[en] Thorium hydride was studied using NMR techniques. Relaxation times of protons and deuterons in Th₄H₁₅ and Th₄D₁₅ were measured over a wide temperature range. Different diffusion processes in different temperature regions were observed. In the range 417 < or approx. = T (⁰K) < or approx. = 526 the activation energy for hydrogen (or deuterium) diffusion was calculated to be E/sub a/ approx. = 14.7 kcal/mole. The pre-exponential factor tau₀ was calculated to be tau₀ approx. = 10^-14 sec for hydrogen, and tau/sup D/₀ approx. = √ 2tau/sup H/₀ for deuterium. The frequency of the quadrupole interaction of the deuterons ν/sub Q/ was found to be in the range 37.4 < or approx. = 43.2 kHz. The electronic contribution to the relaxation in samples of ThH₂ and Th₄H₁₅ was calculated from spin-lattice relaxation-time measurements at low temperatures (78 < or = T < or = 300 ⁰K). While in ThH₂ this contribution can be given as (T₁T)/sub e/ = 567 +- 30 sec ⁰K in the above temperature range, that of Th₄H₁₅ has been found to be temperature dependent. Analysis of this temperature dependence and that of the Knight shift (measured by Lau et al. permitted an estimation of the hyperfine fields of the s and d electrons at the site of the proton. In view of the NMR results it is suggested that f electrons are not present in a significant amount on the Fermi level