Open-tube capillary electrophoresis has been applied to the separation of restriction fragments of DNA with a Tris-borate buffer containing 7 M urea and 0.1 % sodium dodecyl sulfate. The importance of sample pretreatment and of the injection of heated samples has been demonstrated. In one separation, a DNA restriction fragment mixture from 72 to 23 130 base pairs (DRIgestTMIII) (molecular weight range from 4.6 · 104 to 1.5 · 107) has been electrophoresed in 10 min on a column of 15 cm effective length. Over 600 000 plates have been obtained for individual peaks. Several of the peaks have been identified, by spiking slab gel electrophoretically purified components. Other examples of restriction fragment separations are illustrated in this paper. The results of this study when further validated with full characterization of individual species, open up the possibility of rapid restriction enzyme mapping. © 1988.