Integration of knowledge regarding the relationship between stress and illness into clinical practice has been slowed by a lack of clarity in the definition of stress and the difficulties involved in rapid assessment of stress in a busy office setting. The stimulus, response, and interactional models of stress are discussed, and the development of a new stress measure, the Brief Encounter Psychosocial Instrument (BEPSI), is detailed. The reliability of this six-item instrument is demonstrated (Cronbach's alpha .80). Validity is measured through correlation with a variety of instruments measuring stress, including depression (r = .52, P less than .001), anxiety (r = .61, P less than .001), life change (r = .56, P less than .001), bodily expression of stress (r = .56, P less than .001), and a total stress score (r = .67, P less than .001). The BEPSI also demonstrated appropriate negative correlations with family cohesion (r = .29, P = less than .01) and support (r = .31, P = less than .01). When the single open-ended item is strongly positive, 77 percent of patients also score high on the BEPSI. A negative response to the same question corresponds to a low BEPSI value 52 percent of the time. Suggestions are made regarding clinical and research applications.