High-resolution infrared laser spectroscopy is used to study hydrogen fluoride solvated in helium nanodroplets. The results clearly show that the vibrationally excited HF (v = 1) does not relax on the time scale of the experiments (0.5 ms) and that the large linewidth of the R(0) transition (0.43 cm(-1)) results from rotational relaxation. A large de electric field is applied to induce a Q(0) transition, providing an accurate value for the rotational constant of HF in solution (19.47 cm(-1)), only 2% smaller than in the gas phase.