It is widely held belief among bedouins that common linguistic characteristics point to a common genealogical origin. Bearing in mind the importance attached to racial origin amongst bedouins, it is not surprising that they should be keen observers of the dialect of their own and neighbouring tribes. My investigations of the bedouin dialects of the North and East of Arabia do indicate that a common geographical origin is often reflected in a uniform dialect. In this area many bedouin tribes seem to have left an original homeland in the west some 200 years ago, so that in the somewhat isolated conditions of bedouin life their dialect retains the characteristics of the speech of their homeland. A particularly striking case of this is the Rashāyida, a tribe which ‘Arab tradition allies to the Hutaim of north-western Arabia. At some time this tribe broke up and many of them moved east to become clients of the Muṭair. Many others however crossed by sea to the Sudan when they acquired new camels and resumed the nomadic way of life. At present, with the increasing prosperity of Saudi Arabia, many of these have returned as immigrant workers or have been repatriated. Their dialect, however, after a period of perhaps 150 years' separation, is still recognizably of the Najdī type. It would not be possible for dialectology to verify bedouin genealogies; nevertheless, it can be seen that it might support traditions about the earlier location of tribes, since historical sources are not very informative for the medieval period in the Arabian peninsula.