Parasitism by sporocysts was associated with a slight decrease in triglycerides and fatty acids in host digestive gland cells suggesting that the parasite digests, absorbs, and metabolises fats of host origin. An increase in phospholipids and a marked increase in the incorporation of acetate-1- 14C in parasitised digestive glands may be the result of attempted cell regeneration. The parasite had less monoglycerides, triglycerides, and fatty acids but took up more palmitate-1- 14C than the host. Sterols and sterol esters are more concentrated and more readily synthesised in the parasite than in the host. The relatively high level of phospholipids in the former may be related to number of cercariae within the sporocysts.