Pulsed field capillary electrophoresis in ultradilute solutions of sieving polymers has been used to separate nucleic acid fragments as long as 1.6 million base pairs. Hydroxyethyl cellulose solutions are used for separations in the size range 8000-50,000 base pairs. Longer chain nucleic acids are separated in mixed hydroxyethyl cellulose/poly(ethylene oxide) solutions. Separations are rapid (12-13 min).