The very excellent papers which have preceded this presentation have described several methods of identification of viruses following isolation and have emphasized the necessity of accurate methods of isolation and identification. Dr. Herdis yon Magnus in particular has mentioned several methods of diagnosis by the technique of measuring serum antibodies in acute and convalescent sera which are used particularly as diagnostic tools when virus isolation is impossible. In addition, serum antibody studies have had application in research such as in studying the response to vaccination. I would like to describe a technique which is different from any of those mentioned by Dr. von Magnus; namely, the fluorescent antibody technique which we, in our laboratory, are particularly interested in at the present time. We are still in the process of comparing our results obtained by this technique with results obtained by other techniques to be absolutely certain that we may rely upon them entirely and by themselves. This seems highly likely at the present time. There are many advantages to the fluorescent antibody technique, one of which is that is serves both for isolation and identification and for an evaluation of serum antibodies. A second advantage is that it is a rapid procedure enabling one to obtain final results in a few hours rather than after several days as is the case with certain other procedures. Isolation and Identi]ication o/Virus. For the isolation and identification of enterovirus, we use the direct method of fluorescent microscopy. For instance, a stool specimen suspected of harboring the agent is processed in the routine manner and inoculated into several tissue culture tubes in which small eoverslips have been placed so that the cells grow on