The problem of heat or matter transfer for a bed of spherical particles has been fully solved by Amundson. In this paper we consider the modifications which must be made in steady-state solution when the bed may consist of irregularly shaped particles. Considering the case of diffusion limitation of a first-order reaction, it is shown that the results for all shapes will lie close together if the characteristic dimension of the particle is taken to be upsilon(p)/s(x), the ratio of its volume to its external surface area.