We conducted a prospective case-crossover study to assess the association of particulate air pollution with onset of nonfatal myocardial infarction (MI). Patients who had survived MIs between February 1999 and July 2001 were identified based on the Coronary Event Registry in Augsburg, Southern Germany. The study included 851 MI subjects with known date and time of MI who had survived the first 24 hours and had completed the Registry's standard interview. Of these subjects, 691 provided case and control information for subject-specific MI triggers collected by a diary assessing the 4 days before symptom onset. The exposures of interest were the total number concentration (TNC) of particles as an indicator for ultrafine particles and the mass of particles with an aerodynamic diameter no larger than 2.5 microm (PM2.5). We conducted conditional logistic regression analyses using different control-selection strategies in a case-crossover approach, and Poisson regression analyses of the time-series data.