Severe acute respiratory syndrome (SARS) virus caused a severe outbreak in several regions of the world in 2003. The virus is a novel coronavirus, which may have an origin in wild animals such as civet cats in southern China. Its genome structure, gene expression pattern and protein profiles are similar to those of other coronaviruses. However, distinct patterns of several open reading frames in the SARS virus genome may contribute to its severe virulence. The potential mutability of the coronavirus genome may pose problems in the control of future SARS outbreaks. The mechanism of SARS pathogenesis may involve both direct viral cytocidal effects on the target cells and immune-mediated mechanisms. The life cycle of the SARS virus is largely unknown; however, based on the analogy with other coronaviruses, several potential targets for antiviral development are identified. Vaccines offer an important preventive measure for possible future recurrences of SARS, but the prospect for their development is still unknown because of the uncertainty regarding the role of immune responses in SARS virus pathogenesis. The comparative studies of other coronaviruses offer insights into the understanding of SARS virus.