The aim of this study was to analyze how lending outcomes have responded to the introduction of a credit bureau in Guatemala's microfinance market. In August 2001, a major microfinance lender began to install hardware permitting branches to communicate information with the bureau, but did not inform borrowers of the use of the bureau. A randomized training campaign was conducted in which 5000 borrowers were informed of the use of the system, how the bureau worked, and the opportunities and risks it presented for them. Institutional data from the lender and bureau was then used to track how a variety of lending outcomes emerged from this structure in which asymmetric information was reduced on the two sides of the market at two different points in time. It was thus possible to disentangle the supply- and demand-side impacts of credit market information, and identify separately the roles of adverse selection, moral hazard, and incentives on group composition.