The saprobic values and indicator weights used in the Slovenian saprobic system are reappraised using data from the 1990 to 95 river quality surveys of Slovenia. The conceptual basis of the reappraisal is described and then formulated mathematically. The analysis is based on 1,106 biological samples and covers 300 taxa. The results are expressed in terms of revised saprobic values and indicator weights that mirror the ones previously assigned by ecological experts. The most significant differences between original and revised values are highlighted and discussed. It is concluded that: (a) the revised values and weights are more representative of their 'true' values than are the original values and weights, but that it would be premature to consider them definitive; (b) the analytical method provides a sound data-based approach to the revision of saprobic values and indicator weights; and (c) the method could help to improve and harmonise the various saprobic systems currently in use across Europe.