To determine the feasibility and cost-saving potential of substituting outpatient for inpatient cardiac catheterization, 986 consecutive procedures were studied at a large referral hospital. Patients were classified prospectively as to their eligibility for outpatient cardiac catheterization according to published guidelines. Resource consumption was recorded, and cost savings were then calculated by analyzing the specific supply and personnel costs that could change as a result of inpatient versus outpatient status. Of the total of 986 patients who underwent diagnostic catheterization, 240 (24%) were outpatients, 279 (28%) were inpatients but had no exclusion criteria for outpatient catheterization and 467 (47%) were inpatients who had one or more exclusions for outpatient catheterization. The most common reasons for exclusion from outpatient catheterization were congestive heart failure (22%), unstable angina (15%), noncoronary heart disease (14%), recent myocardial infarction (11%) and severe noncardiac disease (9%). Inpatients with no exclusions for the outpatient procedure tended to be sicker than outpatients because they were older (p = 0.002), had a lower ejection fraction (p = 0.009) and had more triple vessel coronary artery disease (p less than 0.0001). The cost of the catheterization procedure itself was not different between inpatients and outpatients. Laboratory testing was more frequent among inpatients, however, and "room and board" costs were significantly higher. Although the difference in hospital charges for inpatients and outpatients was $580, a rigorous analysis indicated that the potential cost savings was only 38% of this amount, or $218 per eligible patient.(ABSTRACT TRUNCATED AT 250 WORDS)