Bacillus cereus shows two distinct types of food poisoning, recognized as the diarrhoeal syndrome caused by enterotoxin and the emetic type caused by heat-stable emetic toxin. Since the latter accounts for the majority of B. cereus foodborne illness in our country, it is necessary to examine the emetic toxin producing activities as well as biochemical confirmations and serotyping tests of isolated organisms. Standard methods for detection of B. cereus emetic toxin are oral challenge in mammals or microscopic assessment of vacuole formation in HEp-2 cells. Because of their requiring specific facilities or skilled techniques both methods create difficulties in some laboratories. In place of them, evaluation of tetrazolium salt MTT assay has previously been described. We studied colorimetric cell metabolic assay in HEp-2 cells by tetrazolium salt WST-8 which produces a water-soluble formazan. This method resulted in equal or higher sensitivity than vacuolation assay. We suggest the application of WST-8 assay as a method for detection of B. cereus emetic toxin.