To understand the interaction between internal control mechanism and the mar- ket for control, using a di¤erences-in-di¤erences methodology, we examine CEO turnover following an exogenous decline of takeover threats? second generation of antitakeover legislation in the U.S. Di¤erent from previous research using only time series variation in CEO turnover, we ?nd that, compared to a control group, the sensitivity of CEO turnover to performance increased for the ?rms a¤ected by the laws. The increases are both statistically and economically signi?cant. We also ?nd that the increases in the sensitivity of CEO turnover to performance are concentrated in the ?rms with bad internal governance. Our results suggest that internal control mechanism and the market for control may be substitutes instead of complements.