Neurologists in Colorado and California were asked the methods they use to test for apnea when determining brain death. Most (65.1%) of 129 respondents simply observed the patient for respiratory efforts for 3 minutes or less while off the ventilator. Only 22.5% measured arterial carbon dioxide, 12.4% used a published recommended rigorous method for testing for apnea, and 11.6% did not test for apnea. Clinicians in full-time academic practice more frequently used the rigorous method. The data indicate that methods used most often in the communities surveyed are less rigorous than published guidelines.