The primary objective of this study was to assess the acute effects for both cold and warm air running on pulmonary function testing and the diagnosis of exercise-induced bronchospasm (EIB). Subjects (n = 12, 8 men, 4 women) were distance runners (25.91 +/- 4.91 milesxwk) with mean age 30.2 +/- 5.1 years, mean height 179.0 +/- 11.5 cm, and mean weight 77.1 +/- 15.7 kg. Subjects first performed a maximal oxygen test on a motor-driven treadmill to assess Vo2max and maximal heart rate (MHR). On 2 subsequent days and within a 1-week time period, subjects ran 8 minutes in random order either on an outside 478.2-m course or on the treadmill at 6% grade. Speed was adjusted under both conditions to elicit 85-95% of MHR achieved on the Vo2max test. All tests were conducted in the month of January to maximize the potential for a cold climate. Pulmonary function test was performed immediately prerun, immediately postrun, and at 5, 10, 18, and 30 minutes postrun. There was no significant difference in any of the pulmonary function tests over time for cold vs. warm running (p > 0.05). Also, the pattern of change over time for the pulmonary function variables was not significantly different by condition (p > 0.05). Although group comparisons were not significant over time and for any variable between the 2 conditions, 7 of our subjects (58.3%) at some point postexercise exhibited a change that would be considered a positive response and diagnostic of EIB. Cold running produced significantly more positive responses (75%) than warm running (25%) (p = 0.001). It is concluded that healthy individuals need not be concerned about the acute effects of cold air exercise on the lungs. Also, physicians need to be vigilant in prescribing medications and should use strict, objective criteria when doing so.