One hundred and sixty isolates of ectomycorrhizal agarics, boletes, and related gasteromycetes were examined for 25 morphological and biochemical characters. A wide range of analytical methods are available with which to obtain efficient summaries of the patterns of variation present in data such as these. Agglomerative clustering of 156 isolates and 18 characters for which no data were missing resulted in partitions of the sample corresponding to recognizable taxonomic and ecological groupings. Key characters useful for delimiting these groups are highlighted by means of divisive clustering and classification trees. For example, boletes (Boletinus, Suillus, Xerocomus) and related gasteromycetous allies (Pisolithus, Rhizopogon, Scleroderma) are distinguished by the production of pigment on media containing high levels of glucose. Numerical taxonomic analyses of cultural characters thus can be useful for examining taxonomic relationships, as in the way in which these characters support not only the close relationship between boletes and some gasteromycetes but also the generic circumscriptions of genera such as Laccaria and Lactarius. However, the taxonomic level at which cultural characters prove most effective must be evaluated carefully, in view of the possibility that, in response to selection, cultural characters have evolved in parallel in separate clades. Thus, ecological as well as taxonomic groups were also recognized. Species of both Hebeloma and Laccaria failed to produce pigment, tolerated low temperatures, and metabolized urea. This suggests that great care must be taken in using cultural characters in phylogenetic studies.