The practice of men swapping daughters for wives or nieces as daughters-in-law is evident among the Bedouin. Although this pattern has its roots in ancient Arab culture and is a unique exception to theories of exchange marriage (EM), there is little reference to the circumstances of its occurrence in the anthropological literature. This article reviews the background of and suggests explanations for this practice. EM is shown to be a strategy that largely serves the desire for upward mobility of small and hence lowly graded groups of agnates. The article demonstrates how EM operates in an olden 'urfi setting, dominated by patrilineages, while shar'i courts tend to oppose it. We argue that, although it entails structural implications, this behavioural pattern does not have a structural end.