Chronic illness exerts a lasting and pervasive influence on personal experience of the world. It is commonly viewed as a phenomenon to be coped with, requiring an adaptive response on the part of an individual. Chronic illness, however, is a culturally-influenced tool which in itself can be used to organize and implement an adaptive response to personal experience. Employing Hallowell's concept of the self in the behavioral environment, the uses of a chronic folk illness, 'high-pertension', for personal adaptation are discussed. Data from research on health beliefs about hypertension and illness behavior in a sample of 60 older African-American women in New Orleans are presented. 'High-pertension', a chronic folk illness related to the biomedical 'hypertension', and involving blood and 'nerves', is described. Health beliefs and illness behavior associated with high-pertension are considered as part of an individual's total effort at adaptation within the behavioral environment. These points are made: (1) Chronic illness can be used as a means to express one's self in relation to the behavioral environment. (2) Chronic illness can be used to manipulate and manage the relation of self to environment. (3) Chronic illness can be used to legitimize and announce role change. These uses are available to the individual by virtue of social interaction, cultural precedent and the chronicity and meaning of the illness itself. For persons in a severely stressed, constrained, and disadvantaged social position, as are many older African-American women, chronic illness offers one of the few means of controlling the behavioral environment available to the individual. Although in anthropology and biology we speak of adaptation in terms of human groups, we are ultimately considering person-environment fit, that is, personal adaptation. Chronic illness can be a part of a culturally-influenced adaptive response.