Gastrothermometer is our own dewice developed with technical assistance of Suzuken developmental devision and Sugiura research industry. With the use of this equipment, the surface temperature of gastric mucosa can be estimated precisely to the extent of 1/100°C. The source of light is Machida RX 500 lighting model with cooling and heat-proof attachments. The fiber optic light transmitting bundle is attached to the FGSBL (operating fiberscope for gastric mucosa biopsy) by means of a connector. The thermister is introduced through this fiberscope into the stomach as its tip being touched to a certain portion of gastric mucosa under the deflector control. Precise temperature changes are detected by double bridge method. The electric pulses are amplified and recorded on pen-writing recorder. Patients submitted to this study are 9 cases of gastric cancer, 57 ulcer, 28 polyp, 1 atypical epithelium, 2 gastritis verrucosa and 6 atrophic gastritis (total cases of 104). In gastric cancers, temperature distribution was found to be inconstant ranging from 7/100°C to 20/100°C. In gastric ulcers, temperatures in central fossa were lower than those in surrounding red zone and prominent areas in active stages. This temperature difference became less significant as diseased areas turned out to be recovered. The average difference was 15/100°C-18/100°C in active stages and 0°C-2/100°C in scar stage. In some cases of gastric ulcer, a reversed temperature difference was noted in scar stage ; it was slightly higher in central zone than in surrounding areas. Higher temperature was noted on the top of gastric polyp than on stems and basis. It was slightly higher on stems than on basis. The larger the polyp, the greater the temperature difference was noted. Ac-tual survey of the temperature difference ranged from 8/100°C to 1/100°C. There was no temperature difference between submucosal tumor and normal mucous membrane. In erosive lesion of gastritis verrucosa. it revealed 1/100°C lower in central fossa than in peripheral areas. In gastritis atrophicans, temperature difference seemed to be more variable with the progress of atrophy. In conclusion, assuming that the temperature difference corresponds with the character of the disease, we designate them as cancer pattern, ulcer pattern and polyp pattern. Precise changes of temperature in diseased area can well represent patho-physiological phenomenon which may be influenced by blood flow, tissue metabolic activity and other factors.