Abstract: The stochastic ray radiosity method is a radiosity method in which no form-factors are computed explicitly. Because of this, the method is very well-suited to compute the radiance distribution in very complex diffuse environments. In this paper we present an extension of this method which will provide a significant reduction of computational cost in cases where accurate knowledge of the illumination is needed in only a small part of the scene. This is accomplished by computing a second quantity, called importance, during the radiance computation. Importance is then used to modulate the patch sampling probabilities in order to obtain lower variance in relevant regions of the scene.