We utilize a unique pair of experiments to isolate the ways in which reductions in asymmetric information alter credit market outcomes. A Guatemalan microfinance lender gradually started using a credit bureau across its branches without letting borrowers know about it. One year later, we ran a large randomized credit information course that described the existence and workings of the bureau to the clients of this lender. This pairing of natural and randomized experiments allows us to separately identify how new information enters on the supply and the demand sides of the market. Our results indicate that the credit bureau generated large efficiency gains for the lender, and that these gains were augmented when borrowers understood the rules of the game. The credit bureau rewarded good borrowers but penalized weaker ones, increasing economic differentiation. (C) 2009 Elsevier B.V. All rights reserved.