I examine the extent to which accounting information is reflected in market prices at different points in time. The efficient market hypothesis implies that price always reflects (value-relevant) accounting information, based on the assumptions of rational investors and costless arbitrage. I examine the time-series relation between price and value in two studies which are motivated by potential shortcomings of these assumptions. First, there is significant debate regarding the rationality of equity investors during the late 1990s. I therefore contrast the historical time-series relation between price and value with that of the 1990s, and show that the historical tendency of price to converge towards value breaks down during this period. Second, I examine the impact of the lack of close substitutes - an arbitrage cost - on the time-series relation between price and value. I find some evidence of a positive association between this arbitrage cost and both the level and the duration of the disparity between price and value. My results provide empirical support for the hypothesis that price requires time to reflect (accounting) information and has implications for research that assumes that prices are measured without error.