Study of the crystallization behaviour of some alkali or alcaline earth silicate glasses. The authors have used the Johnson-Mehl-Avrami equation to describe the glass-crystal transformation. They have established a relation between activation energy, E, and a parameter, m, linked to the reaction mechanism and the DTA curves. The calculated values of these parameters agree well with thw literature data. This shows that the devitrification mechanisms are linked to the structure of the glasses.