The kinetics of release of dipicolinic acid and calcium from Bacillus stearothermophilus spores and the rate of increase of colony count have been shown to be determined by conditions of time, temperature and pH. The apparent activation energies for release of dipicolinic acid, calcium and colony count increase were similar. The results support the hypothesis that breaking of dormancy involves a rupture of dipicolinic acid bonds and that the nature of these bonds rather than the dipicolinic acid content determines dormancy and resistance.