This article reads Genesis 18-19 in the light of the principal of exchange at work in ancient religious belief concerning divine justice. Genesis 18.1-15 and 19.1-29, as examples of the well-worn tale of the divine visitor, are narrative expressions of confidence in a divine justice that rewards the kind and punishes the inhospitable. In the dialogue of 18.6-33, Abraham explicitly raises the question of divine justice, but complicates it by also exploring the possibility of divine mercy. The second divine visitor tale in Gen. 19.1-29, in which Sodom is justly destroyed while Lot is spared out of mercy, shows that Yahweh operates according to more stringent ideas of justice than humanity would wish.