SummaryAdultFasciola hepaticawere placed intraperitoneally into rats which had been sensitized by an oral infection of 20 metacercariae given 3–5 weeks previously. Implanted flukes were recovered at intervals during the next 24 h. Wax embedded sections of flukes and surface impressions of attached cells were examined by light microscopy (LM). Flukes were also examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In all stages, post transplantation, increased secretory activity was noted at the tegu‐mental surface both by the blebbing of membrane and the formation of microvilli. Monitoring of the surface by SEM revealed attachment of very few cells (less than 100/sq mm) in the first hour. By TEM some of these were found to be eosinophils. At 1.5 h local palisading of cells, mainly eosinophils, occurred. Many of these degranulated at a distance from the parasite. Between 2 and 4 h many more neutrophils and macrophages were found, with fewer eosinophils. In the period up to 4 h the tegumental syncytium became charged with abnormally high concentrations of secretory granules and the surface membrane was maintained often enclosing apparently damaged areas. No cells penetrated the syncytium at this stage. Between 4 and 12 h the number of secretory granules in the tegument declined. Around 12 h the remaining granules contributed to the formation of large irregular microvilli. It was at this stage that neutrophils, macrophages and occasional eosinophils moved into the syncytium and began to lift it from bene