This paper examines the performance of the leading methods for setting capital requirements for securities firms' trading books. Tests are conducted on a large sample of UK equity market makers' books over a substantial number of periods of equity market stress from 1985 to 1995. The comprehensive and building-block approaches, favoured by US and European regulators, fail to provide effective cover. Only portfolio-based, value-at-risk (VaR) type models are efficient in providing appropriate levels of capital to cover the position risk of equity trading books.