Polymorphonuclear leukocyte activity was compared with the incidence and severity of ventricular arrhythmia evaluated by Holter electrocardiographic monitoring in 21 patients with acute myocardial infarction. A positive correlation (r = 0.706) was seen between peripheral polymorphonuclear leukocyte count and the amount of leukotriene B4 produced by A23187 (20 microM)-stimulated polymorphonuclear leukocytes on the first hospital day (p less than 0.01). Patients were divided into 3 groups according to the severity of ventricular arrhythmia: no or mild (unifocal, maximal hourly ventricular premature complex rate less than 30, n = 6), moderate (maximal hourly ventricular premature complex rate greater than or equal to 30 or multifocal, n = 6) or severe (R on T, greater than or equal to 2 consecutive ventricular premature complexes or ventricular fibrillation, n = 9). Polymorphonuclear leukocyte count and its leukotriene B4 production were increased with the increase in severity of ventricular arrhythmia among 3 groups. Polymorphonuclear leukocyte count (13,300 +/- 900/microliter, mean +/- standard error of the mean) and its leukotriene B4 production (194 +/- 24 ng/10(7) cells) in patients exhibiting severe ventricular arrhythmia were significantly increased compared with those in patients exhibiting no or mild ventricular arrhythmia (10,300 +/- 1,000/microliter, p less than 0.05 and 120 +/- 21 ng/10(7) cells, p less than 0.05, respectively). Enzymatically estimated infarct size in the latter patient group was significantly smaller than those of the other 2 groups, between which there was no difference in infarct size. These results suggest that polymorphonuclear leukocyte activity is closely related to the incidence and severity of ventricular arrhythmia during the early phase of myocardial infarction.