Activation of Caspase-8 initiates apoptosis in mammalian cells. The NutriCulture Colorimetric Caspase-8 Activity Assay Kit provides a simple and convenient means for assaying the activity of Caspase-8 that recognize the sequence IETD. The assay is based on spectrophotometric detection of the chromophore p-nitroanilide (pNA) after cleavage from the labeled substrate IETD-pNA. The pNA light emission can be quantified using a spectrophotometer or a microtiter plate reader at 400- or 405-nm. Comparison of the absorbance of pNA from an apoptotic sample with an uninduced control allows determination of the fold increase in Caspase-8 activity.