Cryocrystallography with oil - an old idea revived

A method is described that permits the cooling of protein crystals without the use of conventional cryoprotective agents. Covering the crystal completely with highly liquid dry paraffin oil (Merck) prevents ice formation. It is suggested that this method, because of its simplicity, be tried as a first choice in cryocrystallography, since it does not require the growth or soaking of crystals in solvents which could disturb the packing by diffusing into the crystal.