Abstract: A method of preparing purified cyclosporin H includes dissolving cyclosporin A in a first organic solvent and heating the first organic solvent in the presence of an acid catalyst; adding a base to the first organic solvent; recrystallizing cyclosporin H in a second solvent; and purifying the recrystallized cyclosporin H via chromatography to obtain purified cyclosporin H, while excluding recrystallizing the cyclosporin H in the presence of ether. In a further aspect, the method includes, after adding the base and before the recrystallizing, mixing the first organic solvent with a solvent more polar than the first organic solvent, separating the first organic solvent, and drying the first organic solvent. Cyclosporin H prepared as described herein was found to be biologically active, unlike that prepared using a previously-described method.