We produced mammalian expression vectors encoding the SARS coronavirus (SARS-CoV) accessory proteins with or without the fluorescence protein tag and cell lines with stable expression of these proteins. 2. The cellular localisation and function of the SARS-CoV accessory proteins was determined. 3. SARS 6 and SARS 8b proteins are localised to the endoplasmic reticulum and nucleus/cytoplasm, respectively, and both proteins stimulate host cell DNA synthesis.