Fluctuations in demand cause some plants to exit a market and other to enter. Would eliminating these ‡uctuations reduce plant turnover? A structural model of entry and exit in concentrated markets is estimated for the ready-mix concrete industry, using plant level data from the U.S. Census. The Nested Pseudo-Likelihood algorithm is used to …nd parameters which rationalize behavior of …rms involved in repeated competition. Due to high sunk costs, turnover rates would only be reduced by 3% by eliminating demand ‡uctuations at the county level, saving around 20 million dollars a year in scrapped capital. However, demand ‡uctuations blunt …rms’incentive to invest, reducing the number of large plants by more than 50%.