Two different oral tetrazepam (CAS 10379-14-3) formulations (Tetrazepam-ratiopharm film-coated tablets as test preparation and tablets of a reference preparation marketed in France) were investigated in 20 healthy volunteers in order to prove bioequivalence between these preparations. A single 50 mg oral dose was given according to a randomised two-way crossover design in the fasted state. Blood samples for determination of tetrazepam plasma concentrations were collected at pre-defined time points up to 96 h following drug administration. A washout period of 14 days separated both treatment periods. Tetrazepam plasma concentrations were determined by means of a validated LC-MS/MS method. Values of 3873.08 ngh/ml (test preparation) and 3930.69 ngh/ml (reference preparation) for the parameter AUC0-infinity demonstrate an nearly identical extent of drug absorption. Maximum concentrations (Cmax) of 482.08 ng/ml and 465.14 ng/ml were achieved for test and reference preparation. Time to reach maximum plasma concentration (tmax) was 1.39 hours for both preparations. Cmax and AUC0-infinity-values were tested parametrically by an analysis of variance (ANOVA). Bioequivalence was concluded if the 90% confidence intervals of the T/R-ratios were in the range of 80%-125% for AUC0-infinity and 70%-143% for Cmax. Based on the results obtained in this study, bioequivalence between the test and the reference preparation was demonstrated.