The purpose of this study was to develop and test an instrument for analyzing interpersonal responsiveness in small groups. A category system was constructed comprised of two "functional" response categories and five "dysfunctional" categories which identified certain behaviors as likely to foster or interfere with "effective" relationships. To judge the reliability of the category system, data were collected and analyzed from scorings of randomly selected recordings of group interaction. Its validity was established by applying a "known-groups" technique to samples of the group interaction segments judged to be either "effective" or "ineffective." Analysis of results indicated that the effective groups had more content responses and fewer impervious, tangential, or ambiguous responses. These results agree with previous studies which indicate that all the dysfunctional response forms in the category system are identified with family or individual psychopathology. New findings in this study indicate that imperviousness and tangentiality frequently occur in groups with no known pathology; and that projective, inadequate, and ambiguous responses are so infrequently found in "normal" groups as to suggest that they may be genuine indicators of communicative pathology. (Author/JM)