Abstract: A system is disclosed for the rapid and cost-effective sequencing of DNA. There are three principal components of the system: (1) a microreactor, which prepares DNA sequencing "ladders" using solid-phase techniques, preferably in capillary tubes whose volumes are on the order of 10-1000 nanoliters, preferably 10-200 nanoliters; (2) a microfabricated electrophoresis capillary separation unit; and (3) a fluorescence detector with single-mode optical fibers interfaced directly to the electrophoresis capillary. The system is suitable for a highly multiplexed, automated DNA sequencing device Typical. steps in sequencing are as follows: (1) PCR amplification of a DNA template in microtiter dishes using labelled primers, e.g.