This paper examines market risk in four demutualised and self-listed stock exchanges: the Australian Stock Exchange, the Deutsche Borse, the London Stock Exchange and the Singapore Stock Exchange. Daily company and MSCI index returns provide the respective asset and market portfolio data. A bivariate MA-GARCH model is used to estimate time-varying betas for each exchange from listing until 7 June 2005. While the results indicate significant beta volatility, unit root tests show the betas to be mean-reverting. These findings are used to suggest that despite concerns that demutualised and self-listed exchanges entail new market risks that merit regulatory intervention, the betas of the exchange companies have not changed significantly since listing. However, market risk does vary considerable across the exchanges, with mean time-varying betas of 0.56 for the Deutsche Borse, 0.66 for the London Stock Exchange, 0.78 for the Singapore Stock Exchange, and 0.95 for the Australian Stock Exchange.