Organochlorine pesticides have been in use now for about 30 years. As a class of compounds they are not in general readily degradable and they can now be detected in a wide range of samples taken anywhere in the world, including the deep oceans. Organochlorine pesticides are highly fat soluble and it was discovered over 15 years ago that they were accumulated by several forms of life, especially the top predators. Since this discovery a great deal of effort has been spent in attempts to establish to what extent they affect organisms other than the target insect pests. This paper reviews the levels of various pesticides in the sea and the concentration found at different trophic levels in the marine food chain. The levels of accumulation relative to sea water are discussed, together with the known and potential effects that the accumulation levels might have on different types of organisms.