This study was undertaken to determine whether there was an association between air pollutant levels and hospital admissions for congestive heart failure (CHF) in Taipei, Taiwan. Hospital admissions for CHF and ambient air pollution data for Taipei were obtained for the period from 1996 to 2004. The relative risk of hospital admission 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, the number of CHF admissions was significantly associated with the environmental presence of the contaminants particulate matter (PM(10)), nitrogen dioxide (NO(2)), carbon monoxide (CO), and ozone (O(3)) on warm days (>20 degrees C). However, statistically significant positive effects on increased CHF admissions on cool days (<20 degrees C) was observed only for CO levels. For the two-pollutant model, NO(2) and O(3) were significant in combination with each of the other four pollutants on warm days for enhanced CHF admissions. This study provides evidence that higher levels of ambient air pollutants increase the risk of hospital admissions for CHF.