PSEUDOKARST LANDFORMS ON MARS - There are many morphologic features on Mars looking like karstic features, principally in aeolian, glacio-eolian and volcanic formations: etch-pitted terrain, sinkholes aligned along fractures, sinuous alignments of large cavities similar to megadolines, etc. Some of these features are probably collapse features, and some others probably thermokarstic features but it is difficult to understand exactly the process of their genesis, in some cases very different from the process of terrestrial morphologic features. We may evoke the possibility of an underground karst on Mars.