Immunoassay is recognized as a promising method for screening environmental contaminants. Numerous immunoassays have already been developed, and especially the rapidity, sensitivity, and cost-effectiveness of this method are considered as advantageous for screening purposes to reduce sample load for conventional analyses. A particular interesting application involves water quality control with regard to pesticides, for which in Europe a threshold concentration of 0.1 mu g/L applies. An overview is given of the various pesticides for which immunoassays have been developed, including commercially available kits. Pros and cons, applicability, and results of fields tests are discussed. Additionally, a survey is given on further developments for improvement of existing or new immunoassays and on the application of immunochemistry in other embodiments (immunoaffinity chromatography, immunosensors). Particular emphasis is laid on validation and standardization of immunoassays.