THIS REPORT sets forth the evolution of the "Centrifilmer," a precision instrument in which biological fluid suspensions may be exposed in the form of thin-flowing films to controlled ultraviolet irradiation. In recent years, research on practical applications in the production of vaccines has shown that most effective results are obtained when the radiation is combined with other chemical and physical treatments for inactivation. Correlation of this combination-inactivation concept with the resulting improvement in the immunogenic and stability potential of antigens will be discussed.