Consistency and objectivity in red lists are difficult to achieve. Therefore, the new IUCN conservation categories focus on the actual decline of populations using a probabilistic analysis. The application of these categories however, requires information on actual abundance and distribution. As little is known on the population biology of lichens, a national inventory is being carried out in order to assess representative data on frequency and distribution of all species for the official, regionalized red list of epiphytic lichens of Switzerland. According to the number of observations of any particular lichen the minimum absolute frequency will be estimated and a threshold value will define the common species with a low risk of extinction. A pilot study indicates that this would exclude at least 20% of all species from the threatened categories of the Swiss Pre-Alps. As a consequence of the increased sampling intensity of the national survey, analysis of species frequency will result in a higher percentage of lichens assumed to be unthreatened