In the course of this study both the bioavailability and main pharmacokinetic parameters of the glyceryl trinitrate (GTN, CAS 55-63-0) metabolites 1,2 and 1,3-glyceryl dinitrate (1,2-GDN and 1,3-GDN) were to be determined following transdermal application of a glyceryl trinitrate test patch (Deponit 5) and an already marketed reference patch. For this purpose, both patches were examined in healthy volunteers according to a randomized two-way cross-over design, blood samples were withdrawn up to 15 h after start of patch application and the plasma concentrations of both metabolites were quantified using a GC/MS method. The investigation showed the following results: Metabolite 1,2-glyceryl dinitrate: For the area under the curve from time 0 to the last quantifiable sample (AUC(0-Tlast) arithmetic mean values of 23.77 h.ng/ml (test patch) and 27.83 h.ng/ml (reference patch) were found. The corresponding peak plasma levels were 2.45 ng/ml and 2.93 ng/ml, respectively; they were reached after 6.4 h (test patch) and 8.31 h (reference patch). Metabolite 1,3-glyceryl dinitrate: The arithmetic mean values for AUC(0-Tlast) were 3.32 h.ng/ml (test patch) and 3.81 h.ng/ml (reference patch). The maximum plasma levels were 0.35 ng/ml and 0.41 ng/ml for the test and reference preparation, reached after 6.4 h and after 7.86 h, respectively. The statistical comparison (ANOVA, confidence intervals) showed bioequivalence between both patches concerning the metabolites investigated. The typical side effects known after nitrate therapy also occurred in the course of this study.