The transformation exponent s is a characteristic of the mechanism of a reaction and contains information on nucleation rate and type of growth; it corresponds to the Avrami parameter n in isothermal experiments. Two methods for the determination of s from experiments performed at constant heating rate are presented. They consist of plotting either the logarithm of the reaction rate or of the amount transformed versus 1/T, and s can subsequently be calculated from the slope of the initial straight line. The methods are successfully applied to precipitation in Al-6at%Si, GPB-zone formation in Al-Cu-Mg based alloys, and recrystallisation of deformed FCC metals.