The association between exposure to urban air pollution and cardiac or respiratory impairments in susceptible subjects was evaluated in a panel study including 11 patients with chronic obstructive pulmonary disease (COPD), 7 with ischemic heart disease (IHD), and 11 asthmatics resident in Rome (Italy). Patients underwent repeated 24 h Holter EKG monitoring, 12 h pulse oximetry at night and spirometry examinations during 1999 summer and winter. Multiple linear regression models for repeated individual measures (fixed-effect) were used to analyse the relationship between average daily concentrations of pollutants (PM10-2.5, PM2.5 NO2 and O3) and outcome variables, controlling for meteorological conditions, survey period, and week-ends. In the BPCO panel, increasing ambient PM2.5 levels were associated with increased heart rate and decreased respiratory function. In the asthmatic panel, inverse associations between pulmonary function and both NO2 and PM10-2.5 concentrations were observed, as well as direct association between ambient NO2 concentrations and NO in exhaled breath. In the IHD panel an increase of hearth rate variability associated with increasing concentration of PM2.5 was observed.