The detection of weak signals of nonlinear dynamical systems in noisy environments may improve with increasing noise, reaching an optimal]level before the signal is overwhelmed by the noise. This phenomenon, known as stochastic resonance(1,2), has been characterized in electronic(3), laser(4), magnetoelastic(5), physical(6) and chemical(7) systems. Studies of stochastic resonance and noise effects in biological(8,9) and excitable dynamical systems(10-13) have attracted particular interest, because of the possibility of noise- supported signal transmission in neuronal tissue and other excitable biological media, Here we report the positive influence of noise on wave propagation in a photosensitive Belousov-Zhabotinsky(14-17) reaction. The chemical medium, which is subexcitable and unable to support sustained wave propagation, is illuminated with Light that is spatially partitioned into an array of cells in which the intensity is randomly varied. Wave propagation is enhanced with increasing noise amplitude, and sustained propagation is achieved at an optimal level, Above this level,only fragmented waves are observed.