This study aims to assess the impact of the sediment in the potential dredging areas of the Marmara Sea. To that aim, sediments were analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and heavy metals, sources were discussed, and toxicity tests were applied. For assessment, lower and upper limits of Turkish draft regulation (L-TR, U-TR) and UNEP-MAP's guidance document (LCT, UCT), and effects range low and median (ERL, ERM) were used. Total concentrations were found between 562 and 8643 mu g kg(-1) for PAHs, 4-36 mu g kg(-1) for PCBs, and 14-190 mu g kg(-1) for OCPs. The highest n-ary sumation PAH concentrations were measured in Golden Horn, and none of the PAH compounds was above ERM. ERL and UCT were exceeded in Istinye and Golden Horn stations. The highest n-ary sumation PCBs and n-ary sumation OCPs levels were determined in Izmit Bay (IB). sigma PCBs in IB were higher than ERL and L-TR, while sigma DDT were found above ERM and UCT. High concentrations of chromium (similar to 190 mg kg(-1)) and copper (similar to 180 mg kg(-1)) in Golden Horn and mercury in IB (similar to 4 mg kg(-1)) were detected. The highest toxicities were observed in Istinye and Izmit Bay. According to the regulations, none of the sediments can be dumped.