From his personal research undertaken in the subterranean field (natural and artificial cavities) in Shaba (ex-Katanga, in S.E. Zaire) and Rwanda, the author briefly defines the macroclimate of the prospected regions as well as the microclimate of the subterranean habitat (humidity and temperature). A reversible hypothermia has been noticed in the dry season only (from May till August) in eleven species of troglophile Chiroptera belonging to the following families: Rhinolophidae (7 species of Rhinolophus), Hipposideridae (only Hipposideros ruber) and Vespertilionidae (Miniopterus inflatus rufus, Miniopterus schreibersi arenarius & M.s. natalensis, Myotis tricolor). No sign of lethargy has been noticed in the Megachiroptera (Lissonycteris angolensis, Rousettus aegyptiacus leachi), Emballonuridae (Taphozous perforatus sudani), Hipposideridae (Cloeotis percivali australis) or Nycteridae (3 species of Nycteris). There could be correlations between lethargy and breeding if one takes into account the phenomena of late ovulation and delayed implantation. The entry into lethargy is not caused by the scarcity of food. It does not concern all the individuals of a colony or in various populations of a cave. The degree of humidity appears to be more important than the temperature as far as the conditions for hibernation are concerned.