The development of radio immunoassay and its application to the estimation of new substances (e.g. drugs, enzymes, viral antigens, etc.) will shed further light on the various problems which we have discussed in this introductory report. For each group of substances there will no doubt be special difficulties. If these technics have become very popular, this seems to be for two main reasons: the potential selection of individual immune response, and better understanding of the role of the parameters which control the various stages of radio-immunoassay. I am sure that the reports programmed here will provide an important contribution to advances in our knowledge in this promising field.