A total of 104 Damaraland mole-rats was collected in 1988, 1990, 1991 and 1993 from an open water canal in the Otjiwarongo district of Namibia. The mole-rats were apparently dispersing above ground when they fell in and drowned; they had travelled at least 20 m in distance from their natal burrow systems. The dispersing mole-rats of both sexes were significantly larger than 73 animals trapped from a nearby control population. Sequential tooth wear and eruption patterns showed that dispersers were adult animals. There was a bias towards male mole-rats dispersing. Furthermore, in years with lower rainfall (< 300 mm) it was found that dispersal became even more male biased. Eighty per cent of males and 40% of female dispersers showed signs of reproductive readiness, with more males than females being ready to breed. Thus it appears that, in these otherwise totally subterranean mammals, at least one form of dispersal occurs, above ground, and that adult mole-rats are the principal dispersers.