In two experiments employing female and male subjects, respectively, social reactions to "success" were manipulated in an attempt to assess the validity of Horner's Fear-of-Success (FOS) concept as a motivational construct. The use of a single-criterion, dichotomous scoring procedure on a fantasy-based measure of the construct produced moderate to high inter-scorer reliabilities. Although there was only a modest sex difference in the overall level of FOS motivation, significant effects of social reaction were observed in both sexes. The FOS construct appears to have experimental validity when the social conditions sufficient for its arousal are established. The results also raise the possibility that FOS motivation may be a highly situational phenomenon. (Author)