An index for establishing the preservation rate of the riparian ecosystems in Mediterranean rivers (QBR) is presented and its performance in three rivers is tested. The index ranges between 0 and 100 and the final score is obtained through the addition of the scores of four attributes: 1) total cover of riparian vegetation, 2) the structure, 3) the complexity and naturally and 4) the degree of river channel alteration. An application of the index to three Mediterranean basins is presented (rivers Besos, Llobregat and Foix) with 64 sampling points. The index can be easily calculated in the field in few minutes by following a two-page form. This makes QBR a useful tool for monitoring riparian ecosystems in river surveillance, and maybe used, together with biological indicators of water quality, to establish the ecological status of Mediterranean rivers. (Author) 21 refs.