This study was undertaken to determine whether there was an association between air pollutant levels and increased hospital admissions for myocardial infarction (MI) in Kaohsiung, Taiwan. Hospital admissions for MI and ambient air pollution data for Kaohsiung were obtained for the period 1996-2006. The relative risk of hospital admissions 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 models, on warm days (>25 degrees C), statistically significant positive associations were found in all pollutants except particulate matter (PM(10)) and sulfur dioxide (SO(2)). On cool days (<25 degrees C), all pollutants were significantly associated with MI admissions except for ozone (O(3)). For the two-pollutant model, O(3) and carbon monoxide (CO) were significant in combination with each of the other four pollutants on warm days. On cool days, nitrogen dioxide (NO(2)) remained statistically significant in all the two-pollutant models. This study provides evidence that higher levels of ambient air pollutants increase the risk of higher frequency of hospital admissions for MI.