By means of electrical-resistivity measurements Petzold has found that the isochronal recovery spectrum of low-temperature electron-irradiated niobium changes in a spectacular manner if the irradiation temperature is lowered from 8 K to 5 K. It is shown that this observation, which does not appear to be explicable in terms of the so-called one-interstitial model, constitutes strong evidence for the existence of a metastable self-interstitial configuration in niobium irradiated at low temperatures.