Developing chick embryos have been employed rather extensively in this laboratory for the propagation of various infectious agents during the past three years. The method was used to study the effect of the various agents on chick embryos, to find an easy, efficient, and cheap method of rapid propagation, to aid in the identification of the various agents, and to isolate them or to test for their presence in various filtrates, exudates, and tissues. Thus there was no intention of critical tests of the different methods of chick embryo inoculations to determine which method was most satisfactory for each agent employed. However, partial tests or fairly complete tests have been made in some cases and certain conclusions are apparent.