This study was undertaken to determine whether there is an association between air pollutants levels and increased number of hospital admissions for cardiovascular diseases (CVD) in Kaohsiung, Taiwan. Hospital admissions records for CVD and ambient air contaminant data collected from monitoring station in Kaohsiung were obtained for the period 1997-2000. The relative risk of hospital admission for CVD was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. In the single-pollutant model, on warm days (> or =25 degrees C) statistically significant positive associations were found between levels of particular matter of < 10 microm aerodynamic diameter (PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3). On cool days (< 25 degrees C), all pollutants except O3 were significantly associated with increased CVD admissions. For the two-pollutant model, CO and O3 were both significant in combination with each of the other four contaminants on warm days. PM10 and NO2 remained significantly associated with elevated CVD admissions on warm days. On cool days, CO and NO2 remained statistically significant in all the two-pollutant models. This study provides evidence that higher levels of ambient contaminants, particularly CO, increase the risk of increased hospital admissions for CVD.