Measurements of temperatures in 4 deep diamond drillholes drilled from the deepest level of the Fosdalen mines in Trøndelag, Norway, are described. The deepest temperature measurement has been made 1190 meters under the mean surface. The temperature measured at this depth is about 25° C. Mean resiproke temperature gradients are determined for the intervals 30,5- 305 meter and 30,5-1190 m. These two resiproke gradients are found to be 45,6 and 61,0 meters pr.°C, showing a depth-temperature curve that tends to be convex toward the depth axis.