The ultrastructural alterations in the tegument of Fasciolopsis buski in response to incubation in the alcoholic extract of Alpinia nigra were evaluated using transmission electron microscopy. The body tegument of the trematode is composed of an external syncytial layer, musculature, and an inner layer containing tegumental cells. The syncytium comprises various organelles like mitochondria, lysosomes, and tegumentary bodies of the type 2 kind with rare sighting of the type 1. Severe distortion and disorganization of the tegument was revealed in the parasite exposed to the A. nigra extract in the current study. The extent of vacuolization was such that vacuoles proceeded down to the basal lamina causing the syncytium to separate from the tegument at different places. There was depletion of parenchyma material and loss of connecting tubules running down from the syncytium to the tegumental cells causing the cells to be deprived of any proper boundaries. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc.