The thermal damage to the normal tongue was studied. Fortyone hamsters were devided into single heating group (SH) at 42°C, 43°C and 44°C each for 20min. and 40 min., repeated heating group (RH) at 42°C for 40 min. 4 times for 2 weeks, and sham group (SG) with a sensor inserted into the tongue. The tongue was heated by the 13.56 MHz RF capasitive heating system with a pair of applicators 10 mm in diameter filled with jelly.<BR>In SH at 42°C for 20 min., slight to moderate redness and/or swelling were observed and the reaction increased slightly after heating for 40 min. The occurence of moderate redness increased in SH at 43°C for 20min., and the 40 min. heating resulted in the formation of vesicle, erosion and deep ulcer. In SH at 44°C for 20 min., necrosis of more or less than 50% of the heated region was observed, the necrosis involved more than 50% or all of the heated region after 40 min heating.<BR>In RH, slight to moderate redness of the first heating remained until the second heating, but erosion was the severest damage encountered after the successive procedures. In SG, slight redness was observed.<BR>In conclusion, single heating at 42°C was tolerated by the tongue and a little damage and no cumulative effect were noted by repeated heating at 42°C.