Simultaneous application of microwave (MW) heating and mechanical stirring to the Bray-Liebhafsky reaction supports the 'nucleation' theory of nonequilibrium transitions. The opposite effects of microwaves and stirring on the oscillatory reaction dynamics stress the predominant effect of microwaves on the coherence mechanism, preventing in-phase macroscopic oscillations. The obtained results can contribute to the understanding of the mechanism of nonequilibrium transitions on a more general level. (c) 2006 Elsevier B.V. All rights reserved.