The enterotoxic moiety present in the cell-free culture supernatants of Salmonella typhiurium strains (p/536 and p/603) was purified to apparent homogeneity by salt precipitation with ammonium sulphate and successive chromatography through Sephadex G-100 and G-200 columns. It was non-dialysable, heat labile at 90 degrees C and active within pH 6-8. Its activity was completely lost on treatment with trypsin, protease and papain. The enterotoxin appeared to be of high molecular weight (100 kDa) and was highly immunogenic in rabbit. Antigenically, it was not related to cholera toxin, Shiga toxin or the heat labile enterotoxin of Escherichia coli. It did not bind to the GM1 ganglioside. The enterotoxic, delayed permeability and CHO cell elongation activities were attributed to a single protein moiety.