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The aim of the present investigation was to develop a reliable method which can be applied to the measurement of in vitro drug release from nanocarriers. Since the limited membrane transport is one major obstacle to the assessment of drug release with dialysis techniques, the determination of this parameter was our objective. Therefore, a novel drug release automatic monitoring system (DREAMS) was designed to conduct continuous measurements during the dialysis process. Moreover, a mathematical model was used for evaluation of the experimental data. This combination of mathematical and analytical tools enabled the quantification of the total amount of free drug in the system. Eudragit® RS 100 nanoparticles loaded with the model compound 5,10,15,20-tetrakis(m-hydroxypheny)chlorin (mTHPC) were investigated and the drug release was continuously monitored by using a fluorescence spectrometer that is part of the setup. Free drug and drug-loaded nanoparticles were tested to discriminate between the two formulations. In addition, two types of membranes composed of different materials were evaluated and the kinetics of membrane transport was determined. The data obtained from the apparatus were further treated by a mathematical model, which yielded distinguishable release profiles between samples of different compositions. The method offers a promising option for release testing of nanoparticles.