Nitroglycerin has been reported to reduce mortality in patients with acute myocardial infarction. This beneficial effect has been attributed to vasodilation, but it was speculated that part of this effect may be due to altered platelet function. The influence of intravenous nitroglycerin on platelet aggregation was assessed. Eight healthy subjects (aged 22 to 48 years) were studied using filtragometry at baseline, and 3 different nitroglycerin doses. Compared with baseline, aggregation time (which indexes platelet aggregation) increased dose-dependently by 91 +/- 68% (p less than 0.001) at the maximal dose of nitroglycerin (1.1 +/- 0.3 micrograms/kg/min). Plasma concentration-effect relations were observed between nitroglycerin as well as the glyceryl dinitrate metabolites and platelet aggregation (r = 0.6 [p less than 0.002] and r = 0.8 [p less than 0.0001], respectively). It is concluded that increasing doses of intravenous nitroglycerin profoundly and dose-dependently inhibit platelet aggregation. This inhibitory effect correlates with glyceryl dinitrate formation.