Simple gel-based one-step reverse transcription-PCR (RT-PCR) assays, used to investigate patients during the 2003 severe acute respiratory syndrome (SARS) outbreak in Singapore, were found to be as sensitive as commercial and in-house real-time RT-PCR assays. The detection limit was approximately 1 genome equivalent (GE) per 5 microl PCR mixture. One PFU of SARS coronavirus was estimated to be 258 +/- 46 GE.