Sheep were experimentally infested with the larval stage of Taenia multiceps. On Day 36 postinfestation 2 animals were treated intraperitoneally with mebendazole at 40 mg/kg body mass. Mature viable coenuri were present in the cerebra of both these animals when they were killed on Day 114. From Day 36-Day 49 3 animals were treated daily per os with mebendazole at 100 mg/ kg body mass. At autopsy 1 animal had a developing coenurus in the cerebrum while the other 2 animals were not infested. The drug thus had no effect on the development or viability of the coenuri by either of the 2 routes of administration. When a coenurus from a sheep treated intraperitoneally was fed to a cestode-free dog, 5 adult T. multiceps were recovered from the animal 21 days later. The larvae of this cestode undergo some development in extraneural tissues but rarely attain a size of more than 2 mm before they die and degenerate. The pathological changes in these degenerate lesions are briefly described.