[en] Two crystal structures of dehydrated Ag⁺ -and Tl⁺ -exchanged zeolite X (Ag₂₇Tl₆₅ -X and Ag₂₃Tl₆₉ -X) have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21(1) .deg. C (a = 24.758(4) A, a = 24.947(4) A, respectively). Their structures were refined to the final error indices R₁ = 0.055 and wR₂ = 0.057 with 375 reflections, and R₁ = 0.058 and wR₂ = 0.057 with 235 reflections, respectively, for which I> 3σ(I). In the structure of Ag₂₇Tl₆₅-X, 27 Ag⁺ ions were found at two crystallographic sites: 15 Ag⁺ ions at site I at the center of the hexagonal prism and the remaining 12 Ag⁺ ions at site II' in the sodalite cavity. Sixty-five Tl⁺ ions were located at three crystallographic sites: 20 Tl⁺ ions at site II opposite single six-rings in the supercage, 18 Tl⁺ ions at site I' in the sodalite cavity opposite the D6Rs, and the remaining 27 Tl⁺ ions at site III' in the supecage. In the structure of Ag₂₃Tl₆₉-X, 23 Ag⁺ ions were found at two crystallographic sites: 15 at site I and 8 at site II'. Sixty-nine Tl⁺ ions are found at four crystallographic sites: 24 at site II, 17 at site I', and the remaining 28 at two III' sites with occupancies of 22 and 6