Among 150 prospectively investigated patients with acute myocardial infarction (MI) and 150 control patients matched for age, sex and admission date, acute respiratory symptoms occurred in 42 MI patients and in 23 control patients (p less than 0.02). Matched-pairs analysis gave an odds ratio for a respiratory syndrome of 2.2:1 for MI. The statistically significant association of minor respiratory syndromes and the onset of MI must be further investigated to determine whether there is any pathogenetic relation of respiratory symptoms, presumably virally induced, to the onset of MI.