Abstract Two series of offretite and omega were modified by NH 4 + exchanges, on the one hand, and by sequential steaming and acid leaching, on the other hand. X.p.s. were used to quantitatively and qualitatively analyze the surface of these modified solids. The superficial AI concentration significantly differs from the bulk one in synthetic solids. The greatest modifications arise from acid-leaching treatments. Both steps are found to induce scattered effects on the superficial composition. The surface of hydrothermally dealuminated offretites often contains relatively more AI than does the bulk, whereas dealuminated omegas generally display. AI-depleted surfaces. In a sequence of thermochemical treatments, the former steps are suggested to influence the latter. Qualitative analysis has proven the dependence existing between the composition and the countercation involved, on the one hand, and the electronic properties of the constituting elements, on the other hand. No linear increase of the BEs was observed along our modification pathway. Extrafraamework species, which are supposed to be mainly cationic, are responsible for the superficial enrichment of modified zeolites. This enrichment does not always occur during steaming treatments, but also during acid-leaching ones.