The impacts of organic micropollutants, substances in very low concentrations between ng l-1 and g l-1, in aquatic systems are of growing concern in the scientific community. Organic micropollutants are pharmaceuticals, industrial chemicals, personal care products or pesticides. All these substances can have an impact on the environment. Especially the spreading of antibiotic resistant bacterias and genes is alarming. Legal guidelines, which regulate the release of organic micropollutants in the environment, only exist in Switzerland, requiring an average micropollutant elimination of 80%. In the European Union a monitoring programm exists, which investigates the current pollution. In general organic micropollutants can be removed through adsorption (PAK/GAK), AOPs (advanced oxidation processes) and membrane filtration. The ruling mechanisms of the elimination of organic micropollutants through membrane filtration are size exclusion, adsorption and electrostatic repulsion. ^In this work the retention of different organic micropollutants (sulfamethoxazol, carbamazepin, diuron, bisphenol a, bezafibrate, estrone, estriol, ethinylestradiol, ibuprofen, diclofenac) for four different types of membranes, namely microfiltration, ultrafiltration, nanofiltration and reversed osmosis, were investigated. The testing device “Memcell Classic“ is fabricated by the german company “osmo- membrane systems“. In six test series the influence of substance specifics (molecular weight, hydrophobicity/hydrophily, dipolmoment), the characteristics of the feed (concentration, DOC, pH-value) and the operating parameters (pressure, recovery, fouling) were examined. Concerning the spread of antibiotic resistances in WWTP, further tests were made to investigate the retention of free bacterial DNA in membrane filtration systems. Reversed osmosis membranes showed the highest eliminations of more than 90%. ^Nanofiltration membranes also showed removal rates up to 90% , except for diuron and bisphenol a (only 60% removal). Ultra- and microfiltration are not suitable for elimination of orga- nic micropollutants. The collected datas showed the main mechanisms for the removal of organic micropollutants. Microfiltration retains substances mainly through adsorption, whereas for ultrafiltration also electrostatic repulsion is important. The elimination of organic micropollutants with nanofiltration and reversed osmosis is based on size exclusion and electrostatic repulsion. Free bacterial DNA could be removed for more than 90% with all types of membranes, except microfiltration.