An investigation in the bioequivalence of a new tablet formulation with 5 mg isosorbide dinitrate (CAS 87-33-2, ISDN 5 von ct) was performed in a two-way cross-over study with 18 subjects. The relative bioavailability with respect to a reference preparation for AUC related to isosorbide dinitrate was 107.5% and for Cmax 112.5%. A positive decision for bioequivalence derived from the usual confidence intervals for both parameters related to isosorbide dinitrate and the metabolites isosorbide-2-nitrate and isosorbide-5-nitrate, respectively. The difference in tmax showed no clinical relevance. The new formulation was bioequivalent to the reference.