In order to detect and type dengue viruses in serum specimens, four type-specific downstream primers were designed for use with a consensus upstream primer in a reverse transcription and polymerase chain reaction (RT-PCR) assay. RT-PCR using these five primers amplified NS3 gene fragments of diagnostic sizes of 169, 362, 265 and 426 base pairs for dengue virus types 1, 2, 3 and 4, respectively, but not for Japanese encephalitis, Kunjin and yellow fever viruses. The conventional two-step RT-PCR procedure was simplified by combining RT and PCR in a single-step format with a "hot start". This RT-PCR protocol was applied successfully to dengue virus-spiked serum and dengue patient serum samples, and could detect as few as one PFU of dengue virus. This assay offers a rapid, specific and sensitive molecular technique for the simultaneous detection and typing of dengue viruses.