The root-knot nematode, Meloidogyne javanica, incorporated (1)C from its host after exposure of the plant to (1)CO. This uptake was relatively slow and was not detected in nematodes exposed to a labelled plant for periods of 2 and 4 h, but was after 24 h. Nematodes were grown in plants previously infected at weekly intervals to provide animals at various stages of growth. Plants were harvested 24 h after exposure to the label and the rate of incorporation per unit area of nematode was measured. This rate was found to be related to the nematode's physiological age and reached its peak at the time egg-laying commenced, after which it started to decline. The results support the hypothesis that the nematode functions as a metabolic sink.