To Validation the protein inhibition bioassay for measuring active shiga toxin we flurometrically measured inhibitionn of gfr expression in transduced vero cell and compared it to measuring vero cell dehydrogenase activity by colorimetric quantification of the accumulation of MLT formazan formed after the reduction of MTT. As shown in fig3 both bioassays showed significant differences between increasing concentrations of stx2 ranging from 0.01ng/ml to 100ng/ml