On six sites in the "Hogeveense Polder", an area used for bulbculture situated west of Lisse, samples of surface water have been taken monthly during the period august 1989-january 1990. These samples were investigated for the presence of 67 pesticides and related substances. A total of 18 compounds was found in one or more samples. One compound, 2-aminobenzimidazole, could not be evaluated ecotoxicologically due to lack of data. Indicative Maximum Acceptable Risk Levels (MAR's) have been exceeded one or several times for 7 of the 18 compounds viz. aldrin, carbendazim, diazinon, 1,3-dichloropropene, endrin, heptachlor and malathion. For 6 out of 7 (except 1,3-dichloropropene) the indicative MAR was exceeded in all cases that the compound was present in a sample. The values "kwaliteitsdoelstelling 2000" given in the "Derde Nota Waterhuishouding" have been exceeded for 5 compounds viz. carbendazim, diazinon, 1,3-dichloropropene, gamma-HCH and malathion. For carbendazim, diazinon and malathion this value was exceeded in all cases that the compound was present in a sample.