Ready-to-use colorimetric substrate for caspase-4 and related caspases that recognize the amino acid sequence LEVD. Caspase-4 and related caspase activity can be quantified by spectrophotometric detection of free pNA (l= 400 nm) after cleavage from the peptide substrate LEVD-pNA, using a spectrophotometer or multi-well plate reader. The ready-to-use caspase substrate provides an economic alternative for large volume users.