Abstract The way people choose and use different forms of medical treatment in settings in which there exists competing systems of medicine has long attracted the interests of social scientists, physicians and social planners. Studies of this problem area have mainly been impressionistic, ethnographic and/or anecdotal. Lack of a common set of definitions and methods of procedure has hampered empirical study of factors prompting differential use of facilities. We first review this literature and then describe our attempt to systematically compare the way ethnic groups use physicians and lay curanderos in the Chiapas Highlands. A set of concepts and a method of procedure which proved effective is reviewed. A longitudinal design was employed and women of Ladino and Indian background periodically interviewed in depth regarding illnesses experienced during the preceding two weeks. In this report, we concentrate on the role of type of symptoms in the choice of medical practitioner.