Anthropogenic activities have contaminated stream sediments around the world with toxic metals. In Portugal, the Ave river basin, draining to the northwestern Portuguese shelf, is heavily contaminated. The Ave river course and its tributaries are located in one of the most populated regions of the country with intensive agricultural and industrial activities, which effluents have been discharged directly into the local stream. This paper reports results obtained in the analysis of superÐcial sediments collected at the Ave estuary and along the river course within a distance of about 50 km during February 1993. In order to account for seasonal variabilities occurring in the estuary, stations located in this region were also sampled in August 1993. A total of 16 sediment samples were analysed as pressed pellets by energy-dispersive X-ray Ñuorescence spectrometry for 15 elements. The trend of the elemental contamination was evaluated as a function of the location, taking into account external factors that may inÑuence that distribution (tributaries, industries, etc.) and anthropogenic contributions were identiÐed. Comparison of our data with published values considered as the background for non-polluted sediments (average shale) were carried out by calculating enrichment factors. The latter proved that sediment contamination by Zn and Pb exists all over the river basin and also by Cr and Cu in two regions of the area studied. A general depletion in Ni was measured. No signiÐcant seasonal variabilities were detected.