Ozone (O&sub3;) is a pervasive air pollutant that produces pulmonary and cardiovascular dysfunction and possible neurological dysfunction. Young and old individuals are recognized as being susceptible to O&sub3;; however, remarkably little is known about susceptibility with senescence. This study explored the pulmonary, cardiovascular and neurological effects of O&sub3; exposure in adult (4 m) and senescent (20 m) Brown Norway rats exposed to 0 or 0.8 ppm O&sub3; for 6 h, 1 d/week, for 17 weeks. Ventilatory function was assessed 1 and 7 d after each exposure (Buxco). Heart rate, blood pressure (tail cuff) and motor activity were measured biweekly. Blood, aorta and bronchoalveolar lavage fluid (BALF) were analyzed 24 h after the last exposure for pulmonary inflammation, serum biomarkers and aorta mRNA markers of vascular disease. Measures of normal ventilatory function declined following each O&sub3; exposure in both adult and senescent rats, however, senescent rats took weeks to exhibit a decline. Evidence for residual respiratory effects of O&sub3; 7 d after exposure in both age groups was observed. O&sub3; had no effect on either heart rate or blood pressure, but decreased motor activity in both age groups. BALF indicated mild neutrophilic inflammation and protein leakage in adults. Age affected 17/58 serum analytes, O&sub3; affected 6/58; 2/58 showed an age-O&sub3; interaction. Leptin, adiponectin, lipocalin and insulin were increased in senescent rats. Overall, adult rats exhibited more immediate effects of episodic O&sub3; than senescent rats. Residual effects were, however, obtained in both ages of rat, especially for ventilatory endpoints.