The curing reaction of a vinyl ester resin (VER), using methyl ethyl ketone peroxide (MEKP) as initiator and cobalt hexanoate (HxCo) as promoter has been studied by thermal scanning rheometry (TSR) and dynamic-mechanical thermal analysis (DMTA) under isothermal conditions. The gel time, which is defined by several criteria, has been utilized to determine the apparent activation energy (Ea) of the process. Furthermore, an empirical model has been used to predict the change of complex viscosity (eta*) with time, and assuming a first order kinetics, a new value for Ea is obtained independent of HxCo concentration. Finally, the vitrification time has been obtained from DMTA experiments. (C) 2000 Elsevier Science Ltd. All rights reserved.