Slave property rights yielded a source of collateral as well as a coerced labor force. Using data from Dun and Bradstreet linked to the 1860 census and slave schedules in Maryland, we find that slaveowners were more likely to start businesses prior to the uncompensated 1864 emancipation, even conditional on total wealth and human capital, and this advantage disappears after emancipation. We assess a number of potential explanations, and find suggestive evidence that this is due to the superiority of slave wealth as a source of collateral for credit rather than any advantage in production. The collateral dimension of slave property magnifies its importance to historical American economic development.