A theoretical evaluation of the role of microtopography in the phenomenon of mechanically activated dissolution of finely milled minerals has been undertaken. Attention was directed to the role of surface steps produced by fracture and abrasion of milled particles. It was estimated that the activation energy for dissolution at the edge of steps is at least 20% less than that for dissolution from terraces (flat regions) between the edges, leading to enhanced dissolution of steps. The relative rates of dissolution at steps and terraces depend upon the particular mineral/solution process chemistry through the effects of process temperature (T) and the magnitude of the activation energies for dissolution. Enhanced dissolution of particles containing stepped surfaces was modelled by including the fraction, alpha, of dissolution sites on step edges relative to the total number of surface dissolution sites. The fraction, alpha, is expected to be mineral-sensitive through the effects of fracture and cleavage behaviour on step formation. The mean diameter, D-M, of particles subject to enhanced dissolution by microtopography factors was shown to lie in the micron (mu m) to sub-micron range. This range is consistent with particle sizes where enhanced dissolution by mechanical activation has been reported.