This research project involves the dissertation research of a graduate student in ethno-botanical anthropology who will study how members of a Mayan Indian community in southern Mexico select medicinal plants. The project, based on participant observation, field surveys for plants, structured interviewing and lexicographic techniques, represents an in-depth study of the information Mayan Indians need to identify medicinal plants. The researcher will collect medicinal plants with expert Mayan Indians, questioning them as they select (and reject) plants for their pharmacological efficacy. In addition expert Indian plant collectors will be asked to define the characteristics of an already collected set of medicinal plants. The end result will be an in-depth analysis of the cognitive as well as botanical aspects of Mayan Indian medicinal plant use. The dissertation research is in collaboration with other research on the ethnomedicine of Indians in this area, and will contribute to and benefit from this other research. This research is important because understanding how people with a vibrant natural system of medicinal plant use select plants for specific illnesses will advance our knowledge of basic human cognition about health care, and of the medicinal attributes of plants in this area. Recording and preserving indigenous ethnobotanical and ethnomedical knowledge is an important part of preserving global biodiversity.