Telemetered records of radon concentration in well water have been obtained from observation sites along the Pacific coast of Honshu, Japan, since as early as 1977. The accumulated data of two wells in the Tokai district indicate that no unique correlation exists between the water level and radon concentration changes. It is possible that changes in radon and water level are controlled by two different environmental factors, although the long-term trend between the two appears to be concordant. A stronger concordancy of the trend was found between borehole volume strain data and radon data. The concordancy suggests that radon emanation increases when the rocks are subjected to tensional stress.