Investigations into the association of manganese nodules with pelagic sediment in many areas of the deep ocean have mainly considered either (1) the source of metals in nodules, or (2) the occurrence of nodules predominantly at the sediment surface. The second problem is duscussed here. The mechanisms previously proposed have failed to consider that nodules retain their orientation at the sediment surface for several hundred-thousand years, during which time several tens of centimetres of sediment are fluxed down beneath them. Although we have no conclusive evidence, we consider the most plausible explanation for the surface occurrence of nodules to be bioturbation by infauna. ?? 1980 Nature Publishing Group.