The pulmonary function of eight men and eight women (51 to 76 years of age), all non-smokers, was measured before and after 2-hr exposures to filtered air (FA) and 0.60 ppm nitrogen dioxide (NO2). The subjects alternated 20-min periods of rest and 20-min periods of cycle ergometer exercise at a work load predetermined to elicit a ventilatory minute volume (VE) of approximately 25 liter/min. Functional residual capacity was determined pre- and postexposure. Forced vital capacity was determined preexposure and 5 min after each exercise period. VE was measured during the last 2 min of each exercise period, and heart rate was monitored throughout each exposure. The pulmonary function data were evaluated as the percentage change from pre- to postexposure to partially remove the effect of differences between men and women in absolute lung volume. There were no statistically significant (P greater than 0.05) differences between the responses of men and women to FA or NO2 exposure. There were no significant (P greater than 0.05) changes in any variable consequent to FA or NO2 exposure. Our older subjects had responses to NO2 exposure similar to those of young adults, suggesting that, at least for healthy people, exposure to 0.60 ppm NO2 has little effect.