The scanning electrochemical microscope (SECM) has been used to induce and monitor dissolution from the (010) surface of (monoclinic) potassium ferrocyanide trihydrate crystals in initially saturated aqueous solutions containing 3.5 mol dm(-3) potassium chloride. The reaction has been investigated by SECM chronoamperometry in which the potential of a disk ultramicroelectrode tip, positioned close to the crystal surface, was stepped from a value at which no reactions occurred to a value at which the oxidation of ferrocyanide to ferricyanide occurred at a diffusion-controlled rate, thereby initiating the crystal dissolution process. The resulting chronoamperometric characteristics, obtained with a range of tip sizes (electrode radii of 2.5, 5.0, and 12.5 mu m) and tip to crystal separations, demonstrate that the dissolution reaction initially occurs at a rapid rate and quickly attains a steady-state. Quantitative analysis of this data in terms of appropriate candidate dissolution rate laws indicates that the dissolution process is second, rather than first, order in the interfacial undersaturation at the crystal/solution interface. At longer times in the chronoamperometric measurements, the current decreases, suggesting that the crystal becomes less active to dissolution.