Two contrasting notions have been put forward on how social capital may influence individual effectiveness in organizations. Burt (1992) sets forth the informational and control advantages that are possible by building an open network characterized by large numbers of structural holes. In contrast, Coleman (1990) and Simmel (1950) have suggested that network closure, exemplified by large numbers of Simmelian ties, enables actors to develop trust, cohesiveness, and norms which contribute to effectiveness. Simmelian ties are strong, reciprocal ties shared by three actors. It is proposed that an actor's network cannot be dominated by both structural holes and Simmelian ties. Thus, this study examines whether a moderating variable is at work. It is proposed that the actor's task interdependence in the workplace influences the relationship between network closure and individual effectiveness. Actors in less task interdependent environments will benefit especially from the information and control benefits afforded by a network characterized by structural holes. Conversely, actors in highly interdependent environments will benefit especially from the creation of trust and cooperation that result from large numbers of Simmelian ties. Data was collected on 113 subjects in three organizations. Subjects were asked to rate the strength of their relationship with all organization members …