Metals are transferred into the food web by ground-dwelling organisms, among others. This study aimed to identify the most important factors that determine the bioavailability of heavy metals to the spider Pirata piraticus living in the intertidal sediments of the Scheldt estuary (Flanders, Belgium). At five locations, which represent a varying degree of metal contamination and salinity, the superficial layer of sediments was characterised for physico-chemical properties and heavy metal (Cd, Cu, Zn) content and extractability. Spiders were sampled at the same locations and analysed for Cd, Cu and Zn. Higher Cd, Cu and Zn contents were found in spiders on sites with lower total metal contents in the sediment. These sites were closest to the river mouth and were characterised by a higher salinity. Significant, positive correlations were found between the chloride content of the sediments and the Cd, Cu and Zn content of P. piraticus. Similarly, a strong relationship was observed between the ratio of exchangeable Cd and Zn to the total cation exchange capacity and the contents of these elements in P. piraticus. These field data indicated that salinity, cation exchange capacity and exchangeable metal contents were of most importance in determining bioavailability of heavy metals in these intertidal sediments.