Combining the results of two empirical studies, we investigate the role of alters' motivation in explaining change in ego 's network position over time. People high in communal motives, who are prone to supportive and altruistic behavior in their interactions with others as a way to gain social acceptance, prefer to establish ties with co-workers occupying central positions in organizational social networks. This effect results in a systematic network centrality bias : The personal network of central individuals (individuals with many incoming ties from colleagues) is more likely to contain more supportive and altruistic people than the personal network of individuals who are less central (individuals with fewer incoming ties). This result opens the door to the possibility that the effects of centrality so frequently documented in empirical studies may be due, at least in part, to characteristics of the alters in an ego's personal community, rather than to egos themselves. Our findings invite further empirical research on how alters' motives affect the returns that people can reap from their personal networks in organizations. • People who are prone to communal behavior in their interactions with others prefer to establish ties with co-workers occupying central positions in organizational social networks. • We reveal a network centrality bias: the personal network of central individuals contains more communal and pro-social alters than the personal network of individuals who are less central. • This suggests that the advantages typically associated with network centrality are not completely determined by qualities of ego but are, at least in part, due to latent psychological characteristics of the alters in the personal network of highly central individuals. • Corollary: To the extent that more central individuals are more represented in one's network, the professional network of our work contacts will be, on average, more supportive than our own network. [ABSTRACT FROM AUTHOR]