SummaryBithionol administered orally in a single dose of 50 to 66 mg/kg body weight to eight patients with Taenia saginata and eight with Diphyllobothrium latum infections caused the expulsion of long strobilae in all cases. Although the scolex was found in only four cases (50%) of T. saginata and five cases (62.5%) of D. latum infections, stool examinations over follow-up periods of 6 to 41 months showed no evidence of remaining infection. No serious side reactions to the bithionol were seen. Nausea, vomiting, and slight epigastric pain were each noted in one instance.