The introduction of an internal market in the National Health Service (NHS) in the United Kingdom necessitated the use of contracts between purchasers and providers. Little thought was given to the nature of these contracts by policy makers, who appeared to assume that the contracts could conform to the classical, complete model. This paper uses socio-legal and economic theories of contract (which provide an alternative model of relational contracts, in contrast to classical contracts) to explore how realistic that assumption was. An analysis of the institutional context in which the contracts were made is provided, including a legal analysis of the relevant legislation. Contracting by health authorities and GP fundholders is examined, using the results of a recent case study of contracting for district nursing services carried out in a health authority in Greater London. The results show that classical contracting is an inappropriate model for NHS contracts, but that relational contracting is not an entirely appropriate model either. Contracting was found to have increased the accountability of providers in respect of some financial matters, but not in respect of the quality of district nursing services. There are negative implications for the use of contracting in publicly financed health services--hierarchies may be more efficient (as lower transaction costs can be incurred) and possibly more effective in improving quality of care.