In the early 1950s, Herbert Thelen and his coworkers developed a behavioral rating system based on the group dynamic theory of Bion. The methodological work with this system was incomplete. The authors have revised the system and in this article report the new criteria and assessment procedures. A reliability study based on act-by-act scrutiny of 4,343 verbal statements revealed an overall agreement of 77. The range for the emotionality subcategories on specific agreement was from 57 to .67. Mean correlation coefficient for the emotionally charged statements was .80 (n = 12 group sessions). Finally, the validity of the emotionality categories is discussed according to the scientific ideals of logical empiricism and hermeneutics