While bank capital requirements permit a bank to freely substitute between equity and subordinated debt, lenders and investors view debt and equity as imperfect substitutes. It follows that, after controlling for the level of regulatory capital, the mix of debt in capital isolates the role that the market plays in disciplining banks. I document that the mix of debt in capital affects bank behavior, but only when investors can impose real constraints. In particular, the mix of debt reduces the probability of failure and future distress for BHC-affiliated institutions (where the investor has control rights through an equity position) and for stand-alone banks before the Basel Accord (when debt issues included restrictive covenants). However, substituting equity for subordinated debt at the bank holding company level or in stand-alone banks since the Basel Accord (where the investor has few protections) only increases the probability of distress and failure.