An in vitro cultivation model for Salmonella having contact to epithelial cells was developed, which led to an increase in the production of toxic substances. The toxin assay on CHO-K1 cells was used for the determination of the toxic activities. Salmonella strains cultivated in contact with a monolayer of the intestinal cell line IEC-6 produced considerably more toxin than Salmonella strains cultivated on VERO cells. The toxin formed was heat-labile.