It is generally agreed that speculators can make profits from insider trading or from the release of false information. Both forms of stock-price manipulation have now been made illegal. In this article, the authors ask whether it is possible to make profits from a different kind of manipulation, in which an uninformed speculator simply buys and sells shares. They show that in a rational expectations framework, where all agents maximize expected utility, it is possible for an uninformed manipulator to make a profit, provided investors attach a positive probability to the manipulator being an informed trader. Article published by Oxford University Press on behalf of the Society for Financial Studies in its journal, The Review of Financial Studies.