The crystallization in amorphous Fe40Ni40B20 alloy has been studied by electrical resistivity measurement. It shows a three stage compared to the more conventional two-stage crystallization behaviour in many metallic glasses. The Johnson-Mehl-Avrami equation was found to be operative only for 40% transformed crystallized volume for the highest measured isotherm (740 K). The Avrami exponent and activation energy were found to be 1.75 and 53 kcal mol-1, respectively. The low activation energy in the amorphous alloy has been explained by the structural relaxation model. © 1992 Chapman & Hall.