Environmental research at Bayer means the close cooperation between metabolism research, toxicology, ecotoxicology and residue analysis. Trace analysis plays an important role in all of these different departments. It is extremely difficult because very small amounts of the compounds of interest have to be determined besides large amounts of natural or artificial matrix components. These matrix components are extracted from plants or processed products. They also come from soil, water, air or food items of animal origin. Their concentrations exceed the concentrations of the compounds of analytical interest by a factor of 10,000 or more. This causes problems which can only be solved by intensive clean-up, powerful separation techniques and highly specific detection. Soil and water samples from laboratory and field trials are analytically examined starting with the very early development steps of a compound. Thus, its degradation time in soil as well as its potential of transfer into the groundwater can be determined. Only products with excellent environmental properties will be developed. Metabolism research is done with radioactively labelled molecules. Specially designed laboratory trials allow for the exact determination of degradation products of the original compound and for conclusions with respect to its environmental fate. Special analytical techniques help to identify and quantify the degradation products (metabolites). Toxicologists must evaluate the relevance of metabolites and original product for human health. Ecotoxicologists do the same for natural ecosystems. Analytical quality assurance has to be done in both areas. Highly sensitive and specific residue analytical methods are developed for the active ingredient as well as for the toxicologically and ecotoxicologically relevant metabolites. Samples from field trials performed under worst case conditions are analysed by these methods. On the basis of the derived data maximum residue levels (MRLs) and possible use restrictions are set by the authorities. Also analytical methods for the legal enforcement of MRLs in plants and food items have to be provided. The quality of these methods has to be checked by special independent laboratory validations. Even after the registration of a plant protection agent the analytical chemist takes responsibility for his product on the market. For many products monitoring trials are performed. It is checked whether in contrast to all expectations a product has a tendency to contaminate groundwater, soil or food items after long-time use or as a result of accidents or misuse. In such cases analytical results are used to immediately initiate counter-measures. Analytical competence in environmental research grants a maximum degree of safety for consumers, users and nature.