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Nine biological indices based on the macroinvertebrate community inhabiting rivers have been calculated in order to find out which of them is more appropriate to evaluate the qualitative status of the running water for public environmental authorities. The BMWP' score (Alba-Tercedor & Sânchez-Ortega 1988) has been chosen because it is both accurate and precise, and easy to calculate. Some problems derived from sampling strategies are discussed.

A sectorization of the Iberian Peninsula has been obtained on the basis of Helicoidea species distributions. The distributions were analysed by multivariate methods with several qualitative indices, applied to the matrix obtained by dividing the study area into 113 squares of 100×100 km. Dendrograms were obtained by the agglomerative procedure UPGMA. The analysis identified five biogeographical provinces subdivided into subprovinces and sectors. They are as follows. (1) Basque‐Pyrenean‐Catalonian province, with seventy‐nine species and divided into the sectors Basque Septentrional, Basque Meridional, Pyrenean and Catalonian‐Provenzal. This province seems to be a contact area between the three malacofaunistic groupings of western Europe. (2) Province of Castilla la Vieja, with thirty‐six species and divided into Northern and Southern sectors. (3) Mediterranean province, with sixty‐seven species and divided into the sectors of Ebro Valley, Levantine and Baleary. This province is characterized by species of Mediterranean affinities but also contains some species of Septentrional affinities because this province includes the north of the Iberian mountain range, which constitutes a very important refuge area for several species of septentrional origin. (4) Province of Extremadura‐La Mancha‐Andalusia, with forty‐six species and divided into the subprovinces of Extremadura‐La Mancha‐Andalusia and Almería (represented by only one square). The first subprovince is divided into the sectors of Andalusia‐La Mancha and Extremadura‐La Mancha. (5) Lusitanian province, with fifty‐six species, divided into Galician‐Asturian, Portuguese and Duerense sectors, and characterized by species of Lusitanian and Mediterranean affinities.

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