The Netherlands participates in the Joint Assessment and Monitoring Programme (JAMP) of the Oslo and Paris Commissions. This report gives the results of the Dutch contribution to the programme for the year 1999. An overview of the national JAMP programme is given in figure 1. This figure is a map of the Dutch part of the continental shelf showing the sampling locations. Table 1 presents the frequency of sampling and analysis of the various contaminants in the different compartments. Table 2 presents all parameters measured in the different compartments. Data on supporting parameters, nutrients, metals and organic contaminants in water and biota are presented and discussed. Tributyltin in water from inland marinas has been monitored ever since 1990. From the resultant data it is clear that there has been a decrease in TBT since the ban on the use of TBT on vessels measuring less than 25 metres. Recent data on TBT from the monitoring of sediment indicate high concentrations of tributyl and triphenyltin in all Dutch marine waters. TBT concentrations measured range between 10 and 240 ?g TBT/kg sediment normalised to 5% organic Carbon. This implies that the Dutch target value MTR (Maximum Tolerable Risk) laid down in the Fourth National Policy Document on Water Management is being exceeded by a factor 80-300. The highest TPT concentration was about 100 ?g TPT/kg sediment normalised to 5% organic Carbon, whilst the lowest values were below the detection limit (1 ?g TPT/kg). Fish disease monitoring has been included in the programme since 1991, but no results are presented in this report. The report describes the quality assurance programme of the Dutch laboratories and gives details of detection limits and participation in QUASIMEME exercises.