15 years old boy. At first, I thought that he was plunging ranula. But, cyst fluid wad serous (not viscous). So, he was thought to be lymphangioma. 1 KE of OK-432 was injected. The response was bad till 6 weeks after treatment. But, after that, the cyst was gradually reduced. At the period of 6 months after treatment, cyst was clearly disappeared.