We describe the results of an evaluation of marine sediments using chemical measurements and bioassays. Four groups of chemicals, i.e., heavy metals, PAHs, chlorinated aromatic compounds, and tin compounds, were measured at 16 locations in the Wadden Sea, The Netherlands. Extractions of sediments from each location also were assessed using five bioassays. Our objective was to identify chemicals likely to pose biological risks, characterize the relation between bioassay results and particular classes of chemical(s) and determine “clean” reference sites on the basis of the chemical and biological evaluations. A multivariate technique (Principal Component Analysis; PCA) was used to meet these objectives. Results of the PCA indicated that the response of the Microtox Solid Phase bioassay had a positive, significant relationship with the levels of PAHs and organotin compounds. The responses of the other bioassays did not consistently relate to the concentrations of the other measured chemicals. Our findings indicate that the organotin compounds may still be a stressor for aquatic invertebrates in the Dutch Wadden Sea. On the basis of the chemical and biological evaluations, four sites (Dantziggat, Malzwin, Richel and Lauwers) can be considered to be “clean” reference sites.