The distributional data for the metabolic amino acid 3-hydroxy-L-kynurenine as a wing pigment in nymphalid butterflies would suggest taxonomic groupings essentially in contradiction with those resulting from more broad-scale morphological, breeding and behavioral studies; this indicates that the storage of this pigment is a taxonomically relatively unimportant unit character. The inherent danger of taxonomic misuse of single-compound chemical analysis is discussed, as is the significance of the use of the same chemical compound to achieve a given color by several divergent but mutually mimetic forms.