The thermal behaviour of Hg1-xMnxTe single crystals is investigated by means of the RBS/channeling technique. The stoichiometry parameter x ranges from 0.08 to 0.2. An important release of Hg atoms is observed after annealing in hydrogen atmosphere at 240 °C for 10 min. Backscattering spectra for crystals with x = 0.2 revealed quite a sharp Hg edge proceeding towards greater depth with increasing annealing temperature, the shallower region being completely depleted of Hg. Somewhat different behaviour is noticed for samples with x < 0.1. Although the Hg edge is also observed, the intensity of the Hg portion of the spectra diminishes with increasing annealing temperature or time. The latter effect is also observed for all samples after the second and further annealings. The examination by means of the optical microscopy reveals the presence of small cracks and pits which are apparently formed upon annealing. The Hg release through the crack walls is therefore responsible for the lowering of the Hg portion in the backscattering spectra.