EXISTING attempts to determine the economic importance of the interstate slave trade of the ante bellum South have sought to establish two main propositions: (a) This trade augmented the westward flow of population and made a net contribution to the movement of people from where they were less valuable to where they were more productive; (b) it brought profits to the planters in the older slaveholding states and thereby probably prolonged slavery by preventing voluntary manumission. Efforts to support these propositions have taken the form of (1) comparison of the age distributions of slaves in selling and in receiving states, (2) comparison of hiring rates and selling prices for male and for female slaves, (3) efforts to determine the number of slaves involved in the interstate trade, and (4) the often-repeated assertion that some planters profited greatly from the sale of slaves, an assertion accompanied in extremely rare instances by attempts to estimate the importance to slaveholders of this source of income. I shall show that, though in several instances they have produced some authentic information about the domestic slave trade, the four approaches have not substantiated the two central propositions. Furthermore, my investigation of alternatives to existing institutional arrangements provides additional evidence against the two main propositions. Scattered among published sources are components of evidence for a valid proposition about the interstate slave trade: If the older states had to supply population for development of newer areas, it was to the advantage of the exporting states that this be accomplished by the sale of slaves; on the other hand, newer regions should have found it cheaper to receive free whites and free whites accompanied by their slaves than to buy slaves.