Oral MR dosage forms cover a large field in drug delivery technology as they can offer various benefits in oral drug administration, MR dosage forms can be designed to influence the rate, extent and site ofdrug absorption by controlling drug release in the lumen of the GI tract. The in vivo performance of oral MR dosage forms is determined by the interplay of various physiological and dosage form derived parameters. Thus, it is achallenge to predict the in vivo drug release behavior from MR dosage forms based on in vitro release rates. T0 design a dissolution-test system that reflects conditions that are relevant to the in vivo conditions of release and has an adequate discriminative power, it is crucial first to classify the MR dosage form and then to choose adequate in vitro test conditions.The aim of the present thesis was to create biorelevant test systems combining biorelevant dissolution media with an appropriate dissolution apparatus, to predict site, extent and rate of in vivo drug release from MR dosage forms. An additional objective was to assess the feasibility of simulating of different dosing conditions in a physiological relevant but as simple as possible manner.