[en] Positron lifetime measurements are used to study the recovery of vacancies in pure and H-doped Nb and Ta after low-temperature irradiations. After 3 MeV electron irradiation the lifetime in pure Nb and Ta increase to tau/sub v/ = 205 psec due to positron trapping at monovacancies. During annealing of the specimens the vacancy migration is observed at 230 K in Nb and at 280 K in Ta. In H-doped specimens the trapped positron lifetime at vacancies is smaller (170 psec in Nb and 180 psec in Ta), which indicates that vacancies are decorated by hydrogen atoms. Hydrogen shifts the vacancy migration up to 380 K in Nb and 450 K in Ta