Peptide sequences consisting of 2-4 amino acids with high affinity and comparatively high specificity to a number of various, physiologically important proteases are known to have been synthetized before. Such sequences with an added C-terminal marker have been widely used as substrates for the quantitative determination of the kind of proteases mentioned above. The method is based on the fact that the marker is split off under influence of the enzyme and that the liberated marker possesses an easily measurable, for instance, optic property which differs from that of the original substrate. The type of markers used until today have mainly been chromophores or fluorophores which can be quantified by photometry or fluorometry.The present invention relates to a new type of markers coupled to known peptide sequences. These markers are luminol or isoluminol which in their free state can be brought to luminate intensely, but lose considerably in luminescence when they are amide-bound to a peptide sequence.The peptide derivatives consist of acyl derivates of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) or isoluminol (6-amino-2,3-dihydro-1,4-phthalazinedione) where the acyl residue consists of an amide-bound amino acid or amino acid sequence with 2-4 amino acid residues and where the .alpha.-amino group is either free of acylated.The greatest advantages of the luminogenic substrates according to the invention are that theyare considerably more sensitive than the previously use chromogenic or fluorogenic substrates and can be used for measuring even extremely low protease concentration;permit measurement of minute final volumes in standard luminometers which also are technically less complicated and, therefore, cheaper than both spectrophotometers and fluorometers; as a result, costs for both analysis reagents and devices can be cut down;permit linear response measurements within a much wider concentration range than is the case with the usual chromogenic and fluorogenic methods;generate markers less sensitive to deactivating interference as, for instance, chemical quenching; this distinguishes them from, for instance, fluorogenic substrates.