The laboratory diagnosis of dengue has largely relied on serological assays, although many different RT-PCR protocols have been reported. Owing to its limited use, the value of RT-PCR in the clinical laboratory has not been fully evaluated. During the outbreak of severe acute respiratory syndrome (SARS) in Singapore in 2003, RT-PCR to detect dengue viral RNA was used as a rapid diagnostic tool to differentiate dengue from SARS among patients who presented to a hospital designated to manage and quarantine SARS cases. A total of 343 results for RT-PCR and 439 results for serology were analysed and compared with the final discharge diagnosis. Our experience indicates that RT-PCR for dengue can be set up rapidly in a clinical laboratory, with very sensitive and specific results for the diagnosis of dengue, particularly in the first 5 days from onset of symptoms.