Previously introduced method for transforming kinetic function expression was applied on the differential form of isothermal Johnson-Mehl-Avrami (JMA) nucleation and growth equation, to determine the duration of the induction period, tau. The assisting function psi = t(m) was used to obtain a new equation, which enables determination of the induction time, tau, along with the Avrami parameter, n. The procedure was tested using a developed computer program on simulated data, experimental poly(ethylene-terephtalate) (PET) cold crystallization data, and poly(ester-urethane) polycaprolactone-diol polymer (PEU) crystallization data obtained from literature. The test results show the validity of developed equations and their applicability for the determination of kinetic parameters, particularly the induction time. (C) 2004 Wiley Periodicals, Inc.