The aim of this study was to analyse thermal inactivation of bacterial spores in the presence of NaCl, with reference to the activation of latent spores and destruction of activated spores. The effect of different concentrations of sodium chloride on thermal resistance of bacterial spores of Bacillus stearothermophilus (ATCC 10149) was investigated. The spores were heated at different temperatures (110-121°C) in aqueous NaCl solutions at concentrations ranging from 0 to 6%. On the basis of the experiments it was found that the presence of NaCl in the analysed medium increased the sensibility of bacterial spores to heating and affected significantly the process of spore inactivation. It was observed that with an increase of NaCl concentration in the medium, at the same temperature, the time required to achieve the desired microbiological purity was shortened.