The effect of the addition of emergency medicine residency on the use of ancillary testing in a teaching hospital's emergency department (ED) staffed previously by emergency medicine board-certified physicians was studied. Prospectively, the utilization of three common ancillary tests (electrolyte levels, X-ray, or electrocardiogram) for four common chief complaints of patients eventually discharged from the ED was evaluated. A 12-month period before and a 15-month period after introduction of an emergency medicine residency program were compared. The mean number of ancillary tests utilized by the ED attending physicians working with residents was compared with the mean number of tests generated by the same physicians (all emergency medicine board-certified) for the same complaints in the year before the residents' arrival. There was no significant difference in test use before and after introduction of the residency (P = .66). Faculty use of tests was also unaffected by the concurrent presence of residents (P = .068). These results show that the use of testing for a sample of common ED complaints was not affected by the introduction of emergency medicine residents to a previously emergency medicine board-certified staff in one community teaching hospital.