Comparative histochemical studies of glycosidase activity were carried out in Clonorchis sinensis, Eurytrema pancreaticum, Fasciola hepatica, Dipylidium caninum, Hymenolepis nana, Ascaris suum, Toxocara canis, Ancylostoma caninum, Trichuris vulpis and Dirofilaria immitis. The enzymes examined were: N-acetyl-beta-glucosaminidase (EC 3.2.1.30), beta-glucuronidase (EC 3.2.1.31) and beta-galactosidase (EC 3.2.1.23). There were variations in enzyme distribution and intensity among the species and also between trematodes and nematodes; no marked positive reaction for these enzymes occurred in cestodes. In some trematodes, the caeca, especially in the brush border, and the tegument, subtegumental cells and testes, were reactive to the enzymes. In nematodes, although there was variation in reactions among species, N-acetyl-beta-glucosaminidase and beta-galactosidase were localized in the hypodermis and lateral cords excluding the excretory canal, and coelomocytes, intestinal epithelium and the walls of the reproductive systems.