In the drinking-water rcgulution of t.he Federal Republic of Germany limit values in thc range of 0.1 pg/l are est,iiblished for pest.icides. Identification and quantihtive determinat.ion of pesticides in this concrntration range reqnirc a very high expenditure concerning analysis, devices and equipment, analyt'ical methods having been available so far only on a limited scale. The sum limit. value of 0.5 yg/l pesticides may create special difficulties. I n general, in view of the approx. 300 possible substances first of a l l a screening has to be proposed conc,erniiig t,he exceeding of limit values based on knowledge from the catchment area and its potential loading a,s the first, step of investigation. Suitable mrthods of determinat,ion nre partly available in gns chromat.0graphy and high-pressure liquid chromatography. Promising in the future development are the biochemical methods of enzyme inhibition (cholinesterase) and of immunoa,ssay with radioactive and erwyine labelling. Neverthelefis, for thc foreseeable futuro st,andard methods will be available only for approx.Two thirds of the total of 300 substances, so t h a t discussing the effectiveness of the limit values should be carried on.