We study the stability of a homogeneous state to inhomogeneous density modulations in a chemical system where the constituents undergo diffusion as well as chemical reaction. The system is autocatalytic: One species activates the recation, while the other is an inhibitor. We show that the stability of the homogeneous state is enhanced, if the activator species is spatially correlated due to interparticle repulsion. (C) 2003 American Institute of Physics.