The role of oxygen and food in the vertical distribution of nematodes was investigated by means of an experiment in which different oxygen and food conditions were imposed on sediment from an intertidal area of the Oosterschelde (The Netherlands). Two treatments and a control were maintained for 5 days. The analysis of the field situation showed that nematodes were the most abundant taxon. Highest densities were observed in the subsurface sediment layer (1-2 cm). The lower abundance in the oxygen and algae-rich superficial layer (0-0.5 cm) could be due to the time of sampling relative to the tides or to biotic factors (e.g. macrofaunal activity). The vertical distribution of the nematode assemblages in the experimental and control treatments proved to be significantly different. An obvious segregation existed between the nematode species assemblage from the superficial (0-0.2 cm) and the deeper layers (0.2-1 cm and 4-5 cm). The occurrence of the first species assemblage is determined by oxygen availability and is independent of food availability. The second species assemblage, adapted to reduced sediment, is attracted by food availability and the addition of limited amounts of oxygen. In general, the combination of food and oxygen seems to be important in determining the vertical distribution of nematodes in this experiment.