The need for further research on the environmental effects of sewage sludge disposed of at sea is examined with particular reference to conditions in the UK. Additional expenditure on monitoring and research appears to be justitied Dy comparison with the cost to dischargers of adopting alternative means of disposal. Research should be directed to improving methods of predicting the effects of increased discharges at selected sites and to understanding the behaviour of specific components of sludge which are not degraded in the sea. It is concluded that improved information should be obtained about (a) relative inputs of pollutants from land-based sources in some areas, (b) the physical processes controlling dispersion, sedimentation, and degradation of sludge particulates, (c) the mobilisation of conservative substances from sludge, and (d) the role of nutrients and other substances in sludge in the development of certain algal blooms.