For some years good communication and collaboration between health and welfare professionals has been emphasized as a desirable goal by both official reports and relevant professions. This is as much the case in mental health as other areas. This paper compares communication and collaboration between social workers and general practitioners (GPs) with that between community psychiatric nurses (CPNs) and GPs. Both social workers and CPNs were based at a community mental health centre, and the contact was interagency (with primary health care). Major differences were found between social workers and CPNs. CPNs were far more likely to contact GPs than social workers, although GPs very rarely initiated contact themselves. Differences reflected different 'philosophies of contact'. Social workers contacted GPs when this could be purposively related to their case management. In addition to this contact, CPNs also made contact to provide GPs with information, reflecting awareness of GPs' long-term continuing care responsibility. The excess of CPN contacts was not limited, but involved a wide range of problems. GPs, however, when contacted, exerted greater influence on social work case management. The article concludes by explaining differences between CPNs and social workers in terms of occupational culture. It suggests, furthermore, that the results arise at least in part from assumptions of team leadership by GPs, and that social workers' and CPNs' behaviour represents different responses to this.