We studied the temperature stability of the endohedral fullerene molecule N@C-60 inside single-wall carbon nanotubes using electron-spin-resonance spectroscopy. We found that the nitrogen escapes at higher temperatures in the encapsulated material as compared to its pristine, crystalline form. The temperature dependent spin-lattice relaxation time T-1 of the encapsulated molecule is significantly shorter than that of the crystalline material, which is explained by the interaction of the nitrogen spin with the host nanotubes.