The fluorine content of certain thermal and ground waters in this district was determined colorimetrically by the use of Neo-Thorin. The temperature and the chloride, bicarbonate and calcium content of the same waters were also determined. It was found that fluorine content ranged from 0.6mg/l to 9.1mg/l in the thermal waters and was less than 0.6mg/l in the ground waters. The positive and linear correlation between the fluorine content and the Cl(-), HC0(3)(-), and Ca(2+) content was considered to be the outstanding characteristic of the thermal waters
of this area. From these facts, it is concluded that the fluorine in the waters at Misasa Hot Springs is originally introduced from the same source as the thermal waters.