The DNA in dormant spores of Bacillus subtilis as well as other Bacillus species is extremely well protected against damage resulting from treatments such as desiccation, heat, oxidizing agents, and UV and gamma radiation. This high degree of DNA protection is a major factor in the survival of spores of these species, not only when subjected to the treatments noted above, but also when incubated under common environmental conditions for many years. Factors that play major roles in overall spore resistance include the low permeability of spores to toxic chemicals and the decreased spore-core water content. However, although decreased spore permeability and water content appear to at least partially protect spore DNA from oxidative damage, these factors seem to play little or no role in protecting spore DNA from heat damage. The major factor preventing damage to spore DNA is the saturation of this DNA with a novel group of small, acid-soluble proteins of the alpha/beta-type whose binding greatly alters DNA's chemical and enzymatic reactivity as well as its UV photochemistry. Binding of these proteins is also a key factor in spore DNA resistance to desiccation, heat, oxidizing agents, and UV radiation.