This study examines how organizational characteristics affect agency participation and centrality in community service networks. We find that the network structure of agency relations varies for administrative and client-related activities among the 69 agencies studied, which include all but the most isolated agencies serving people with physical disabilities in a single community. In identifying structurally equivalent groups using network analysis, we find that all types of agencies except HMOs are found throughout community service networks. Analyses show that among the five types of relations, minimal intergroup activity occurs within funding and planning networks and that organizational size and ownership are the best organizational predictors of network location and centrality. Non-profits are the most central for planning and client referrals, and large agencies are the most central for funding. We explore the implications of these findings, particularly for sustaining cooperation within the service networks and for the role of non-profits and medical providers in the community.