Recently, it has been known that the aminosidine has marked anthelmintic efficacy against tapeworm. In this investigation, aminosidine was used for treating 14 cases with Ciphyllobothrium latum infection and 5 cases with Taenia saginata infection. Aminosidine was administered orally in a single dose of 50 mg/kg, followed by a purge after the treatment. Fourteen patients with D. latum infection and 5 patients with T. saginata infection expelled long strobila in all cases. Although only 7 scolices of 18 worms of D. latum were found in the stool and no scolex of T. saginata was found, follow-up examination for a long period showed no evidence of remaining infection with one exception of D. latum. Mild nausea, vomiting and abdominal pain were observed in only one of 19 cases given aminosidine. But in the other 18 cases, no side effects were encountered. It was concluded that aminosidine is safe, effective therapeutic agent for the treatment of cestodiasis in man.