Dissolution of magnesium fluoride seed crystals has been studied in the absence and presence of some mineral salts under conditions in which the under-saturation was maintained constant and controlled by a specific fluoride ion electrode. Over a range of relative under-saturation, 0.3-0.75, the dissolution reaction appears to be governed by a surface polynucleation process which is markedly inhibited by the presence of additives. The action of mineral salts on the rate of dissolution of magnesium fluoride crystals can be interpreted in terms of a Langmuir-type adsorption isotherm.