Laboratory measurements of Kr and Xe adsorption on samples of ground montmoril-lonite, limonite and basalt at -77 ¿C have been performed. Results suggest that 1) most degassed martian Xe could be adsorbed on a regolith with a large effective surface area, and 2) if this is the case the elemental composition of martian nonradiogenic rare gas (counting that in the regolith) may be virtually identical to that of ordinary chondrites.