Detailed instructions are given for the preparation of a purified and stabilized suspension of vaccinia elementary bodies. This is intended to take the place of crude glycerinated calf or sheep lymph vaccine. The technique consists of a series of procedures involving mechanical disintegration of the skin pulp, maintenance of dispersion by means of a non-ionic detergent, fractional centrifugation and bacterial disinfection. Stability of the purified virus is secured by suspending it in a dilute buffer containing peptone and polyvinylpyrrolidone. Experiments are described which illustrate the remarkable heat resistance of the virus in this suspending medium. The PVP-peptone also serves as an excellent menstruum for lyophilization. Production of this vaccine should be well within the competence of any properly equipped virus laboratory. Clinical trials are in progress.

All the work involved in the performance of the tissue culture assays was carried out by my former assistant Mr Edmund Bischoff. It is a pleasure to acknowledge both his technical skill and his enthusiasm. Mr T. C. Campbell provided the crude calf pulp used in the preparation of some of the purified suspensions.