The purpose of this study was to use a new model of decision making to understand variability in physicians' utilization of diagnostic tests. We studied physicians' recommendations for coronary arteriography in hypothetical patients with chest pain by analyzing responses of 235 cardiologists and family physicians. Thresholds for testing were derived by obtaining estimates of the probability of disease and recommendations for coronary arteriography before and after an exercise test. We found that cardiologists compared with family practitioners had a significantly higher decision threshold and recommended coronary arteriography in fewer patients. These findings suggest that analyzing physicians' decision-making thresholds may be used to characterize differences in the practice behavior of groups of physicians.