Ready-to-use colorimetric substrate for caspase-9/Mch6 and related caspases that recognize the amino acid sequence LEHD. Caspase-9 and related caspase activity can be quantified by spectrophotometric detection of free pNA (l= 400 nm) after cleavage from the peptide substrate LEHD-pNA, using a spectrophotometer or multi-well plate reader.