the observation in 1989 that the q-value of superconducting cavities fabricated from high purity niobium could significantly degrade when these cavities were kept for longer periods of time at temperatures between 50k and 200k became a major concern for accelerator projects employing superconducting cavities. a large number of investigations were carried out at various laboratories and the initial hypothesis expressed in precipitation of a niobium-hydride phase was supported by additional experimental data by other laboratories. the detrimental effect of hydrogen precipitation in niobium has been known for many years, but nevertheless the performance degradations of the cavities came as an unexpected surprise, when a rather uniform additional loss distribution over the whole cavity surface was measured on a temperature map. it was experimentally verified that the q-degradation could be avoided, if the cavities were cooled down quickly through the dangerous temperature region; hydrogen degassing at temperatures above 700(degree)c eliminated the deterioration, but subsequent extensive chemical surface treatment seemed to reverse the process. for large scale accelerator projects like cebaf the cryogenic system might prefer certain cooldown cycles; therefore it is of great interest to determine the exact temperature range which does not effect cavity performance, if a string of cavities were held at these temperatures. in the following we report on the investigation of the q-degradation of a niobium cavity under various conditions. 6 refs