The Geo-referenced Regional Exposure Assessment Tool for European Rivers (GREAT-ER) model was developed as an aquatic chemical exposure prediction tool for use within environmental risk assessment (ERA) schemes and river basin management. The GREAT-ER software calculates the distribution of predicted environmental concentrations (PECs) of consumer chemicals in surface waters, for individual river stretches, as well as representative average PECs for entire catchments. The system uses an ARC/INFO-ArcView (ESRI) based Geographical Information System (GIS) for data storage and visualization, combined with simple mathematical models for prediction of chemical fate. Use of GREAT-ER 1.03 to derive PECs is illustrated for Ethinyl Oestradiol, Paracetamol, Aspirin, Dextropropoxyphene, Clofibrate and Oxytetracycline in three river basins, i.e. Aire (UK), Lambro (Italy) and Rur (Germany). In contrast with household consumer chemicals the transformation of pharmaceuticals in the human body needs to be incorporated in the emission estimation. The "PECinitial" of these pharmaceuticals in surface waters ranges from >1 microg/l (Oxytetracycline and Paracetamol) down to <1 ng/l (Ethinyl Oestradiol). Risk characterization employing PECs or measured environmental concentrations (MECs) and predicted-no-effect-concentrations (PNECs) from available ecotoxicity data is also reported.