We have designed and synthesized fluorescent oligonucleotide primers having improved fluorescence and electrophoretic properties by exploiting the concept of resonance fluorescence energy transfer (ET). These primers carry a fluorescein derivative at the 5' end as a common fluorescence donor and other fluorescein and rhodamine derivatives attached to a modified thymidine within the primer sequence as acceptors. These primers all have strong absorption at a common excitation wavelength (448 nm) and fluorescence emission maxima of 525, 555, and 605 nm. The fluorescence emission intensity of the ET primers increases as the spacing between the donor and acceptors is increased, and of the spacings studied the strongest fluorescence was observed when the number of nucleotides between the donor and acceptors is 10. The electrophoretic mobilities of the primers were also found to be a function of the spacing between the donor and the acceptors, and mobilities of the single base extension DNA fragments generated with primers (F10F, F10J, F10T, and F10R) is 2- to 14-fold greater than that of the corresponding primers labeled with only one dye. The increased fluorescence intensity of the ET primers and the substantially similar mobilities of the DNA fragments generated with the four ET primers allow four-color DNA sequencing on a capillary electrophoresis DNA sequencer using a single laser line at 488 nm for excitation and without applying mobility shift adjustments. With single-stranded M13mp18 DNA as the template, a typical run with the ET primers on a commercial sequencer provided DNA sequences with 99-100% accuracy in the first 500 bases using 8-fold less DNA template than that typically required using T7 DNA polymerase.