In the present study four species of opisthorchoid cercariae are included: the cercariae of Euryhelmis monorchis Ameel, 1938 (Heterophyinae), Caecincola parvulus Marshall and Gilbert, 1905 (Cryptogoniminae), and two as yet undescribed species. Euryhelmis monorchis was obtained from Pomatiopsis lapidaria: Caecincola parvulus from Amnicola (Marstonia) lustrica: and the two undescribed species from Amnicola (Amnicola) limosa and Goniobasis livescens, respectively. All were collected near Ann Arbor, Michigan. Whole mounts of normally emerged and of developing carcariae, fixed in basic lead acetate, and serial sections of infected snails, fixed in Bouin's solution were employed in the studies of Euryhelmis monorchis and of the undetermined species of cercaria from Amnicola limosa. Caecincola parvulus was studied from preparations of normally emerged cercariae and from Bouin's fixed, serially sectioned Amnicola lustrica. The cercariae from Goniobasis livescens were studied from serially sectioned, Bouin's fixed snails. Dilute, aqueous toluidine blue and thionin solutions were used exclusively. Basic lead acetate is a poor fixative and killing agent. However, usable preparations were obtained with hot, saturated solutions of this reagent, followed shortly with 70% alcohol. Metachromatic differentiation following Bouin's solution was excellent. The concurrent decalcification of the shells when snails were fixed in Bouin's made dissection unnecessary.