We analyzed the ordering and impact of the first 171 fee-for-service cardiovascular nuclear medicine procedures at one hospital. The ordering physicians said 72% of the study results were useful and 28% contributed to changes in patient management. Experienced cardiology reviewers, however, felt that only 65% of studies were appropriately ordered, that 97% of appropriately ordered studies provided potentially useful information, and that 12% of all studies made important contributions to appropriate changes in patient management. The revieweres were most likely to rate exercise thallium procedures and procedures ordered by physicians from distant hospitals as being appropriately ordered and having important clinical impact. We conclude that (1) ordering physicians and revieweres may disagree substantially in their estimates of the impact of a diagnostic test; and (2) although a test may yield important information in appropriate patients, its total clinical impact will depend on how often it is suitably ordered and used.