Heavy metal concentrations of surfical sediments around the Istanbul metropolitan area are generally higher than the average shale values, with the highest contents occurring near the confluence of the Istanbul Strait (Bosphorus) with the Sea of Marmara. The metal distribution, together with that of organic carbon, suggests a significant contribution from munipical wastewater discharges. A total of 28 sites were sampled twice, with a 10-month interval (February and December 1996) to assess changes in the sediment composition. Analyses of the two batches of sediment samples suggest no significant changes in Cu, Pb and Zn; increases in Fe and Mn, and decreases in Hg and Ni contents over this time interval. Despite the high population density and industrialization in the area, these sediments have not been significantly contaminated in comparison with similar marine areas elsewhere in the world. This is mainly due to the dynamic two-layer circulation system of the area.