Using a retrospective chart review, we compared the use of chest radiography (CXR) and arterial blood gas testing (ABG) before (pre-P) and after (post-P) initiation of specific ordering guidelines for the use of these studies for patients presenting to the ED with acute asthma exacerbation. We noted the number of tests performed, the indication for the test, and the results when performed. There was a 55% reduction in the number of chest radiographs (85 of 213 patients pre-P had CXR as compared with 40 of 222 patients post-P, P <.001). Of the patients who did not have a chest x-ray in the ED, none had an abnormal chest x-ray obtained after admission or if they returned to the ED within 72 hours. There was a 57% reduction in the number of arterial blood gases post-P (9 of 222 patients) as compared with pre-P (20 of 213 patients, P <.001). Although patients with abnormal ABGs had a discernible indication for testing, all of the ABGs for which no indication could be found were normal. A protocol containing criteria for obtaining chest x-rays and arterial blood gas testing can reduce the use of diagnostic testing, thereby improving ED efficiency without adversely impacting patient care.