The purpose o f the present invention is to proviae: an extract of mtlamed skin from a rabbit that has Deen inoculated with the vaccinia virus, said extract having improved quality stability and a preparation, or the like, which contains the extract as an active ingredient. B y using as an indicator the amount of tyrosine sulphate contained in an extract 01 inflamed skin from a rabbit that has been inoculated with the vaccinia virus, and the amount contained in a preparation containing said extract, the improved quality stability of each production lot of the extract, and the preparation can be ensured. The extract of inflamed skin from a rabbit that has been inoculated with the vaccinia virus, and the preparation containing said extract, which have quality stability that has been improved by such a method, are extremely useful, and have more strictly guaranteed efficacy and safety.
