Histochemical and cytofotometric techniques were used to detect esterase and lipase in the hepatopancreas of the snail Lymnaea truncatula and in larval stages of its parasite Fasciola hepatica. Activities of both enzymes were shown to increase in the infected hepatopancreas, compared with the control. The effect is ascribed by the authors to compensation processes emerging as a defence mechanism in the snail. Both enzymes, esterase and lipase proved to be highly active in tissues of sporocysts, rediae and cercariae, thus demonstrating the larvae to be capable of katabolism of lipids and utilising them as an energy source.