An approach for real-time DNA sequencing without the need for electrophoresis has been developed. The approach relies on the detection of DNA polymerase activity by an enzymatic luminometric inorganic pyrophosphate (PPi) detection assay (ELIDA) (Nyrén, P. (1987) Anal. Biochem. 167, 235-238). The PPi formed in the DNA polymerase reaction is converted to ATP by ATP sulfurylase and the ATP production is continuously monitored by the firefly luciferase. In the sequencing procedure, immobilized single-stranded template was used in a repeated cycle of deoxynucleotide extension. Real-time signals in the ELIDA, proportional to the amount of incorporated nucleotide, were observed when complementary bases were incorporated. An increased signal-to-noise ratio was obtained by substitution of deoxyadenosine alpha-thiotriphosphate (dATP alpha S) for the natural deoxyadenosine triphosphate, dATP alpha S is efficiently used by the DNA polymerase, but is not recognized by the luciferase. As a model, 15 bases of a single-stranded PCR product were sequenced. The possibility for parallel processing of many samples in an automated manner is discussed.