Introduction and Objectives. Pulmonary and cardiovascular responses in healthy volunteers, patients with chronic obstructive pulmonary disease (COPD) or ischaemic heart disease (IHD) were investigated following exposure to the high levels of diesel pollution on London’s Oxford Street. Methods. Using a cross-over design 40 healthy volunteers, 40 patients with COPD and 39 patients with IHD walked along Oxford Street (diesel only traffic) and, on a separate occasion, in Hyde Park (traffic free) for two hours. Cardio-respiratory measurements were performed at baseline and during and after each exposure, alongside personal particulate exposure measurements. Findings. Pulse wave velocity (PWV), a measure of arterial stiffness, increased in healthy subjects 24 hours after Oxford Street exposures started compared to Hyde Park (0.6m/s vs -0.4m/s, co-efficient=0.43, 95% CI 0.25-0.61, p < 0.001). This phenomenon was also seen in COPD subjects 24 hours after exposures started (0.4m/s vs -0.4m/s), with the ‘Oxford Street’ effect statistically significant (co-efficient=0.50, 95% CI 0.33-0.68, p < 0.001). There were no significant changes in PWV seen in the IHD subjects. Healthy volunteers had a 1.6% increase in FEV1 five hours after the start of exposure on Oxford Street, compared to a 7.2% increase in Hyde Park. Similar changes were noted six and 24 hours after the exposure started (co-efficient= -2.13, 95% CI -3.23 to -1.02), p < 0.001). FEV1 in COPD subjects dropped by 2.2% one hour after the exposure started on Oxford Street (co-efficient=-1.36, 95% CI -2.24 to -0.47), p < 0.003). Measurements of impulse oscillometry demonstrated increased airway resistance in subjects with COPD at 5 Hz (R5) of 0.05 kPa/l/s four hours after the exposure started on Oxford Street (co-efficient=-0.03, 95% CI 0.01 to 0.04), p=0.001), and at 20 Hz of 0.02 kPa/l/s 24 hours after exposure (co-efficient=0.017, 95% CI 0.01 to 0.027), p < 0.001). The IHD subjects had significant increases in airways resistance at R5 four hours and 24 hours after the exposure started on Oxford Street (0.07kPa/l/s and 0.01kPa/l/s respectively, co-efficient=0.03, 95% CI 0.01 to -0.06, p=0.015). Conclusions. Vascular dysfunction was observed in all the volunteer groups following exposures on Oxford Street. Volunteers with COPD were observed to have increased airflow obstruction.