Metrics are discussed which are used for the evaluation of bioequivalence of modified-release formulations. In order to ensure the therapeutic equivalence of the compared drug products, it would be important to contrast measures which are additional to area under the curve (AUC) and C max. For delayed-release products, the assessment of lag times is informative. For extended-release dosage forms, comparisons of the half-value duration and the midpoint duration time are useful. For some modified-release formulations with complicated, multiphasic concentration profiles, the comparison of partial AUCs is important. In determinations of the bioequivalence of extended-release dosage forms, investigations performed under steady-state conditions rather than after single dosing can yield enhanced probability of therapeutic equivalence, especially with substantial accumulation of the drug products. In steady-state investigations of bioequivalence, evaluation of the trough concentration and of the peak trough fluctuation is informative.