Activation of ICE-family proteases/caspases initiates apoptosis or other cellular processes in mammalian cells. The Caspase-1/ICE Colorimetric Protease Assay Kits provide a simple and convenient means for assaying the activity of caspases that recognize the sequence YVAD. The assay is based on spectrophotometric detection of the chromophore p-nitroanilide (pNA) after cleavage from the labeled substrate YVAD-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 a treated sample with an untreated control allows determination of the fold increase in Caspase-1 activity.