An investigation of the surrogate assessment of coronary artery disease (CAD) patients' functional capacity was conducted using 193 patient and surrogate rater dyads. Mean age of patients and surrogate raters were 60.4 and 54.4 years, respectively. Patients and surrogates independently completed a brief questionnaire that assessed health and psychosocial factors. The Duke Activity Status Index (DASI) was contained in the patients' questionnaire, while a similar form modified to assess patients' functional capacity was imbedded in the surrogates' questionnaire. Results indicated similar psychometric characteristics and clinical validity for patients' self-report and surrogates' ratings, suggesting that the Surrogate Rating Form of the Duke Activity Status Index (DASI-SRF) is a reliable and valid proxy method of assessing patient's functional capacity when this information may not be obtained directly from the patient. Further, while there were no effects of surrogates' health and psychological characteristics on their ratings of patients' functional capacity, in comparison with other surrogates, spouses were more likely to rate patients higher in functional capacity. Exploration of the patient/care provider relationship via concurrent use of the DASI and DASI-SRF is discussed.