OBJECTIVE The in-vivo performance of oral modified-release dosage forms is determined by the interplay of various physiological- and dosage-form-derived parameters. Thus it is often a challenge to predict the in-vivo drug-release behaviour from modified-release dosage forms based solely on in-vitro release rates. RESULTS For a long time the most common procedure to obtain in-vitro/in-vivo correlations for modified-release formulations was to apply test conditions typically used for quality control on a retrospective basis. Such so-called 'compendial approaches' are typically not biorelevant with respect to volumes, composition and physicochemical properties of the test media and also do not take into consideration the mechanical and hydrodynamic forces that may influence dosage-form behaviour during passage through the gastrointestinal tract. CONCLUSIONS This review provides an overview of physiological conditions relevant to in-vivo drug release and of dissolution models which, based on current scientific findings on human gastrointestinal physiology, have been developed to enable a better prediction of the in-vivo performance of oral MR dosage forms.