A toxin gene (bceT) on a 2.9 kb DNA fragment of Bacillus cereus B-4ac was cloned and expressed in Escherichia coli, and its nucleotide sequence determined. The DNA fragment contained an open reading frame capable of encoding a polypeptide of 336 amino acids with a molecular mass of 41039 Da. The translated product in E. coli exhibited Vero cell cytotoxicity, and was positive in a vascular permeability assay. It also caused fluid accumulation in a ligated mouse ileal loop and was lethal to mice upon injection. These biological activities are considered characteristic of diarrhoeal enterotoxins. We therefore conclude that this gene, designated bceT, encodes one of the enterotoxic proteins of B. cereus which cause food-borne diarrhoea.