A theoretical analysis is developed for diffusion-controlled heterogeneous reaction in a material with a bimodal poresize distribution. A configurational averaging procedure is used to describe a sparse, random network of macropore capillaries contained in a reactive, otherwise homogeneous matrix. The analysis is valid for a wide range of reactivities, and is particularly suited for conditions where reactant concentration varies on a length scale comparable to the diameter of, or the spacing between the macropores. The results depend on the reactivity on the matrix, the void volume of the macropore network, and the macropore to matrix diffusivity ratio. A local effectiveness parameter, which depends on the reactivity and macropore void volume, characterizes the reaction behavior in the material. An exact numerical solution is obtained that depends analytically on the parameters of the problem, and an accurate analytical representation is derived that depends very simply on the local effectiveness, the macropore void volume, and the diffusivity ratio; typical results are presented. The solution reduces to simplified models of the heterogeneous reaction in the low- and high-reactivity limits, where reactant concentration varies on a length scale that is large compared to the macropore spacing or small compared to the macropore diameter.