The objective of this study was to determine both the pharmacokinetic parameters and the bioavailability of two commercial 20-mg isosorbide-5-mononitrate (IS-5-MN) preparations (test and reference preparation) after single oral administration. For this purpose, the test and the reference preparation were examined in 24 healthy male volunteers according to a randomized 2-way cross-over design, blood samples were withdrawn up to 24 hours postadministration, and plasma concentrations of IS-5-MN were quantified by a gas chromatography (GC) method. Both preparations led to peak plasma levels of approximately 360 ng/mL IS-5-MN in the mean 0.76 hour (test) and 0.94 hour (reference preparation) after application; the plasma half-lives were about 5.2 hours, and for the areas under the curve (AUC(0-infinity)), mean values of 2741 (test preparation) and 2742 hour.ng/mL (reference preparation) were found. The statistical comparison (analysis of variance, confidence intervals) of the pharmacokinetic parameters found in the study resulted in bioequivalence of both IS-5-MN preparations. The undesired side effects/concomitant symptoms observed are known to occur after IS-5-MN administration.