A definition of biodiversity is adopted that takes account not only of numbers of species, but also of the degrees of difference among them. The most appropriate measure of species differences is likely to be made in terms of genealogical relationships, as embodied in taxonomic classifications. Five new measures of taxonomic diversity are compared with existing measures of species richness and taxonomic root weighting for prioritising areas for the conservation of biodiversity, using as an example some data for 43 bumble bee species of the sibiricus-group. Although certain of the new measures can be shown to perform better than any existing methods, more extensive trials are needed, and further refinements can be anticipated. We conclude that combining species richness with taxonomic diversity to give a single measure inevitably involves compromise, as either component could be maximised in its own right. Nonetheless, the new prioritisation methods are already capable of giving practical results.