A critical review of existing concentrations of the potential pollutants Hg, Cd, Pb, PCBs and DDT in marine waters, sediments and biota of the global ocean indicates that the highest concentrations are usually found in the most densely populated and industrialized regions which are often located near major river estuaries. In general, present concentrations, particularly those in edible marine organisms, do not give rise for alarm; however, in some cases national and international concentration limits have been exceeded which has caused some concern for human health. In some ‘hot spots’ (e.g. Minamata Bay, Hudson-Raritan Estuary, Los Angeles Bight, Ems Estuary) where measures have been taken to eliminate the sources of contamination, a significant reduction in concentrations has occurred. Reliable temporal data are generally too sparse and have not been collected for a sufficient period to make accurate predictions about the environmental half-life of the contaminants; however, the widespread occurrence of persistent organochlorine residues of PCBs and DDT in remote areas far from known input sources suggests a long residence time in the ecosystem. Spatial data on a global scale are also limited; therefore, it is difficult to draw firm conclusions about long-term consequences of the shift in use of DDT and other chlorinated pesticides towards tropical areas and the southern hemisphere. However, the few reliable data available from these regions indicate concentrations of some organochlorine compounds in marine matrices that are as high or higher than those reported for the northern hemisphere. More data from a much wider area are needed in order to clarify this trend.