This paper discusses the relationship between the public and private sectors in the Unified National Health System (SUS), based on research whose objective was to identify governance strategies and mechanisms for public/private relations in the health sector, considering the search for equity in Greater Metropolitan Sao Paulo, Brazil. Governance was used as an analytical category, with health system regulation as the issue. Municipal and State health secretaries, members of health councils, and SUS staff were interviewed, and the empirical material was classified as: (a) regulatory mechanisms and instruments; (b) power loci; and (c) actors' positions concerning the SUS and its relationship to the private sector. Mechanisms and instruments have been created and used in the municipalities for regulation of their own services. Regulatory measures for the complementary and supplementary healthcare sector are practically nonexistent. There are numerous institutional power loci, seen more as places for submitting demands than as forums for negotiation. Despite some progress, governance appears to be more of a formal issue. Discussion is needed on the relationship between the public and private sectors and its regulation by municipalities in order to improve the health system.