[en] In the Stripa mine, situated in the central part of Sweden, a pilot heater test has been carried out at 348-m level. The type of rock is a granite with a rather high frequency of fractures. A central main heater with a length of 3 m, a diameter of 30 cm and a total power of 6 kW was placed at the bottom of a 10-m-deep borehole. At different radial distances, varying from 0.85 m up to 2.95 m from the heater, stress and temperature changes were monitored. Additional measurements of movements along major fractures on the surface and changes of water inflow in boreholes were carried out. The measured temperature distribution compares fairly well with the predicted. A maximum temperature of 333.9⁰C was measured. The thermal conductivity of the rock mass has been calculated to lambda = 4.8 W/m⁰C. The thermally induced stresses in the rock mass do not correspond well with the predicted values. Results of measurements in boreholes of the in situ modulus are found to be about half of the laboratory determinations. Displacements of major fractures on the floor of the test drift are very small