The introduction of a market mechanism into the National Health service in the UK was underpinned by the belief that decentralised purchasing would both improve the quality of health care provision and restrain spiralling costs, through purchasers exercising their ability to choose between alternative providers. Focusing on budget holding General Practitioners, that is those practices responsible for purchasing hospital services for their practice populations, this paper explores the evolving purchasing behaviour of these professional intermediaries. Drawing on empirical evidence gathered as part of a broader study of the purchasing behaviour of GP Fundholders in Scotland, specifically it examines the key information sources and decisional criteria utilised by these professional intermediaries in selecting health care providers for their practice population. Utilising relational models of market behaviour, it addresses both the contextually specific issue of whether the market mechanism within the NHS is achieving the twin objectives of improving health care provision and restraining cost pressures, and the broader conceptual issue of the purchasing behaviour of professional intermediaries within a service sector environment. © 1996 Taylor & Francis Group, LLC.