Information asymmetries--which occur when one party to a transaction has more or better information than the other party--such as moral hazard or adverse selection, can cause inefficiency, overinvestment, or poverty traps. Unfortunately, they are difficult to identify in practice. This working paper by Dean Karlan, CGD non-resident fellow, and his co-author provides a microfoundation for studying the real effects of credit constraints by identifying the presence (or absence) of two specific credit market failures: adverse selection adverse selection (where sellers lack information) and moral hazard (where buyers or borrowers lack information). The experiment identifies information asymmetries by randomizing loan pricing using 58,000 direct mail offers along three dimensions: an initial "offer interest rate" featured on the direct mail solicitation, the actual interest rate on the loan contract revealed only after the borrower agreed to the initial offer rate, and the interest rate on future loans offered only to those who remained in good standing. Findings show evidence of moral hazard with weaker evidence of adverse selection. A rough calibration shows that approximately 7% to 16% of default is due to asymmetric information problems. This paper is one in a series of six CGD working papers by Dean Karlan on various aspects of microfinance (Working Paper Nos. 106 –111).