The testing of groups of people, under rigorously controlled condition, has considerable potential as a tool of market research, In saying this, I am not referring to the use of small groups (of 6-8 people) for discussion purposes. What I am writing about, however, is a very different use of groups. It has proved-a relatively simple matter to bring ordinary members of the public together in groups of about 40 at a time and to test them on an almost unlimited range of topics - tests of knowledge, assessments of attitude and studies of reactions to carefully prepared stimuli. Taken forty at a time, group numbers can be aggregated to give as many cases as are required. Provided certain serious sampling difficulties can be overcome - and I shall be speaking about this at some length - group work of this kind can be used to provide a valuable supplement to the information gathered through the ordinary survey interview. I am thinking particularly of Information derived through the kinds of test I have just mentioned: tests of knowledge and of ability? assessments of certain attitudes, comparative studies of-reaction under controlled conditions. As a technique, it is relatively inexpensive and has the special advantage of offering quick results. A further advantage of the method is that a full record can be kept of precisely what was said by the test administrator and of precisely what processes the respondents, were put through.