Since hyperthermia was established as one of the treatment modality to cancer, there have been some reports on the effect of the treatment on upper respiratory tract disease. It has been reported that hyperthermia has the effect of antiviral activity, increased regional blood flow and blocked histamine release from mast cell. And some clinical data have supported the favorable effect in patients with nasal allergy. This study was designed to clarify basic mechanism of the effect of hyperthermia in the allergic patients. Authors collected the mast cells from peritoneal and pleural fluid of Wistar rats and treated the cells with temperature of 37℃ and 42℃. After treating the cells with heat, they were stimulated by compoud 48/80 or DNP-ascaris and the histamine release rate(HRR) was measured. The results were as follows : 1) The HRR was decreased in the group treated at 42℃ compared to that at 37℃. 2) The cells stimulated by compound 48/80 after heating showed the decreased HRR in the group treated at 42℃ compared to that at 37℃. 3) The cells stimulated by DNP-ascaris after heating showed decreased HRR in the group treated at 42℃ compared to that at 37℃. 4) The cells stimulated by DNP-ascaris after heating once or twice for 5 or 10 minutes showed the lowest HRR in the group treated twice at 42℃ for 10 minutes. The group treated once at 42℃ for 10 minutes showed lower HRR than the one treated twice at 42℃ for 5 minutes. 5) The cells stimulated by compound 48/80 after heating once or twice for 5 or 10 minutes showed the lowest HRR in the group treated twice at 42℃ for 10 minutes. The group treated twice at 42℃ for 5 minutes showed lower HRR than that treated once at 42℃ for 10 minutes. The results suggested that hyperthermia could block histamine release from mast cells and repeated hyperthermic stimuli could induce mast cells to release less histamine.