The effects of water‐vapor ambients on the solid‐state epitaxial regrowth of ion‐beam‐amorphized, near‐surface layers on single‐crystal CaTiO3have been investigated using Rutherford backscattering‐channeling spectroscopy, time‐resolved reflectivity, and cross‐sectional transmission electron microscopy (TEM). The presence of water vapor in the annealing atmosphere increases the thermally induced epitaxial regrowth rate and, within the temperature range studied (400–550 °C), decreases the activation energy for this process. TEM micrographs from samples which were partially regrown in high‐H2O‐concentration atmospheres revealed uneven amorphous/crystalline interfaces with fluctuations on the order of 5–10 nm. Samples annealed in water‐vapor‐deficient atmospheres exhibited very flat interfaces after partial epitaxial regrowth. The morphologies of these interfaces are explained in terms of a segregation of hydrogen ahead of the regrowth interface. Additionally, it has been determined that the absence of oxygen does not affect the regrowth rate. Samples annealed in oxygen concentrations as low as 10−21atm exhibit growth rates that are identical to those measured for air‐annealed CaTiO3samples. ©1995 American Institute of Physics.