The curing process of diepoxide-triamine systems filled with water and untreated alumina nanoparticles has been investigated. The influence of both types of fillers on the curing process is very similar. This is reflected by a similar shape of the heat flow (HF) and specific heat capacity curves during curing. A catalytic effect of hydroxyl groups in the water and on the nanoparticles surfaces is made responsible for the observed curing behaviour. It turns out that the strength of the catalytic effect depends on the type of filler. The described influence of alumina nanoparticles on thermoset curing is looked upon as being representative for nanocomposites consisting of epoxy thermosets and metal oxide nanoparticles without surface treatment. (C) 2011 Elsevier B.V. All rights reserved.