The development of truncated microtriches in the somatic region of both (a) protoscolices incubated in vitro with two different drugs, i.e. ivermectin or a combination of albendazole and albendazole sulphoxide, and (b) protoscolices removed from hydatid cysts in humans treated with albendazole for 1.5 months is described. Our findings seem to indicate that the development of microtriches is either an indirect effect of treatment with anthelmintics or a possible response to other, as yet unidentified, adverse conditions.