Using high-level ab initio methods, the binding energies were calculated for helium and neon inside the cage-like dodecahedrane molecule C20H20 The binding energy of He@C20H20 is 33.8 kcal/mol, including the change in zero-point energy. The corresponding energy for Ne@C20H20 is 98.3 kcal/mol. The He-3 nuclear magnetic resonance chemical shift is 1.51 ppm, relative to He-3 outside the molecule. The equilibrium constant for He@C20H20 was calculated, and the pressure corresponding to the experimentally synthesized compound is 4 x 10(26) atm.