FEV(1) is recommended for rating the severity of obstructive and restrictive pulmonary diseases, but it only moderately correlates with quality of life, mortality, and functional status. The 6-min walk test (6MWT) has been increasingly used in clinical practice and research studies as an objective measurement of functional status in patients with moderate-to-severe impairment. This low complexity test measures the distance a patient can quickly walk back and forth in a 30-m (100-foot) corridor in a period of 6 min, referred to as the 6-min walk distance (6MWD). The 6MWD, and in some circumstances oxygen desaturation during the 6MWT, are useful to assess response to medical interventions, to assess prognosis in various conditions, and as a single measurement of functional status. Strictly scripted test instructions and encouragement at baseline and at each minute of exercise is vital to obtain reproducible results. The 6MWT is reported using Current Procedural Terminology code 94620 (simple pulmonary stress test). This code is also appropriate for other simple exercise tests, including oxygen titration (if additional parameters are measured), exercise-induced bronchospasm evaluation using pre- and postexercise spirometry, and exercise prescription for pulmonary rehabilitation. Use of code 94620 to bill for services must be supported by significant documentation.