TAME (N_α-p-tosyl-L-arginine methyl ester) is a specific substrate of trypsin. N_α-p-tosyl-L-arginine is released from TAME after tryptic hydrolysis,which reacts with NaOH in the assay mixture and causes the decrease of pH.Using phenol red as the indicator, the PH change of the solution can be monitored by the decrease of the absorbance at 555 nm. The decrease of A₅₅₅ is directly proportional to the amount of trypsin with a linear range of 0.001～0.3 mg.The method is very convenient to use, highly sensitive and specific.