Abstract
Suitability of the laboratory rat and golden hamster as hosts for Hymenolepis microstoma has been demonstrated. Older rats become refractory to infection, and possible physiological changes in the bile have been postulated as the cause of this phenomenon. The early gross pathology of the bile duct in all three hosts is described and is postulated to be caused by a toxic product of the helminth. Occasional deaths in the hamster hosts, accompanied by additional intestinal pathology, have been attributed to extrahepatic occlusion. Characteristics of short-term growth have been established for H. microstoma in the mouse, the rat, and the hamster.