Results of recent research strongly suggest that people find beneficial phytochemicals by selecting plants to use as medicinals and that taste plays a major role in this process. The research reported here involved an experiment performed with Highland Tzeltal Maya of Chiapas, Mexico to determine if bitterness served as a chemical cue for plants appropriate for treating gastrointestinal versus respiratory illnesses. Eight Tzeltal men and two women were asked to taste common medicinal preparations, describe the taste, and provide the name and medicinal use of the source plant. They were also shown dried specimens of the same plants and asked for taste, name, and use. Consensus analysis showed that participants had a good knowledge of medicinal plants and agreed about their use, but could not predict the use of individual plants based on taste alone. Bitterness was not correlated with any particular class of illnesses; probably because there is not enough resolution in human taste to deal with the diversity of chemicals that taste bitter but produce different physiological effects. The role of taste is more likely mnemonic than chemical-ecological, and functions in combination with other plant attributes and illness experiences to facilitate human cognition and communication. Results of this study suggest that prototype theory, in which a few plants serve as best examples of a subset of plants used to treat a group of illnesses, may provide a theoretical perspective for understanding how people reduce informational complexity and reconcile the very different domains of plant classification, epidemiological context, and illness experience.