Aims: To screen for the virulence potential of Aeromonas isolates based on the change in regulation of c-jun and c-fos in the human intestinal tissue culture cell line Caco-2. Methods and Results: Aeromonas cells were added to Caco-2 cells at a ratio of approx. 1 : 1. After 1-, 2- and 3-h incubation at 37 degrees C, mRNA was extracted from the cells and gene expression of two host genes, c-jun and c-fos, quantified. Aeromonas isolates which were pathogenic in the neonatal mouse model demonstrated up-regulation of c-jun and c-fos compared to avirulent isolates. Conclusions: Human cell culture results showed that c-jun and c-fos were predictive of Aeromonas virulence. Significance and Impact of the Study: An Aeromonas relative virulence scale is proposed for use in the testing of Aeromonas drinking water isolates.