The classification of species with respect to their conservation status usi
ng the IUCN criteria is an important process in many countries, providing a
guide for setting conservation priorities. Recent advances have resulted i
n several approaches to dealing with uncertainty in data used to classify s
pecies. These methods demand an unambiguous and transparent logical structu
re for the criteria. We suggest some changes to the ways in which the crite
ria are represented that correct an unnecessary inconsistency and which may
serve to avoid important errors when uncertainty in the data is considered
explicitly. (C) 1999 Elsevier Science Ltd. All rights reserved.