A method is described which employs a continuous flow of medium in the in vitro cultivation of the cyclophyllidean cestode Hymenolepis diminuta. Cysticercoids dissected from beetles were excysted and cultured to adults with proglottids containing developing oncospheres. These results were reproducible. Total length changes of the growing worms were recorded on different days of culture. The medium is a combination of whole blood plasma, Tyrode''s solution, and organic substances. The apparatus for culture maintenance is designed to allow for continuous passage of a small volume of medium over the worms. Worms grown by this method showed normal segmentation and scolices and could not be distinguished from worms grown in rats.