Kuo-toa's Blood

Kuo-Toan's Blood is a quest item needed Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition during chapter 4. The Matron Mother needs this, or the blood of the Elder Brain or the eye of an Elder Beholder for the ritual. It can be acquired from the Kuo-Toan Prince who resides in the caves leading to the surface, which can be entered west in the Underdark Area.

In-game description
"This is the blood of the Kuo-Toan prince."