The present study examined the socio-demographic, clinical, cognitive, social behaviour and social network characteristics of the 97 patients in contact with the COSTAR programme--a mobile treatment and case management service for the long-term mentally ill in inner-city Baltimore. Compared with shorter-contact patients, those in contact for more than one year showed no change in symptoms, or in cognitive or global function. They did manifest improved social function, especially for slowness, personal hygiene and posturing. The long-contact group showed improvements in the quality and quantity of their social networks. Our results suggest that a home-based treatment system can help patients to reverse a vicious cycle of social isolation and to establish supportive social contacts.