To evaluate the novelsubstrate Z-Nle-Lys-Arg-AMC in a complex biological sample that containsother proteases and proteins, the assay of cathepsin B activity inhomogenates of human neuroblastoma cells (SHSY-5Y and SK-N-MC neuroblastoma)and mouse microglial cells (BV2 microglia) compared the use of theZ-Nle-Lys-Arg-AMC substrate to that of Z-Arg-Arg-AMC and Z-Phe-Arg-AMCsubstrates. Here, CTSB is linked to neuroblastoma.