The benthic fauna of a fly-ash dumping ground off the Northumberland coast has been studied in comparison with that of the surrounding natural sediments and a designated offshore spoil ground. Continued ash dumping has resulted in an increase in the silt fraction of the sediments, together with the appearance of pozzolanic aggregates at the sites of greatest dumping, some 3·5 km offshore. The sediments here show a more rapid decline in Eh values with depth. The natural benthic macrofauna represented a typical Echinocardium-filiformis community, giving way throughout the offshore spoil ground to a ‘ Paraonis-Magelona’ community dominated by smaller polychaete species more tolerant of poor sediments, while the stations at the centre of the ash dumping showed an anomalous community structure. The density of the fauna was reduced at the centre of the ash dumping, the worst station yielding only eight individuals in 0·2m. Contours of numbers of macrofaunal individuals and species, of faunistic diversity and biomass, and of meiofaunal numbers all show a similar pattern of some depression along the spoil ground, and greater depression at the ash-dumping centre. Statistical analyses confirm a significant negative correlation between faunistic parameters and ash content. Deposit-feeding species represented a lower proportion of the community at sites of high ash content. The negative correlation between faunistic diversity and ash content was statistically significant over an area of 43 km around the centre of the dumping. The faunistic impoverishment is considered mainly to be a response to the dumping per se, and options for reducing this effect are discussed.