c-Jun N-terminal kinase (JNK) is one of the several main MAP kinase groups identified in mammals. Recent evidences suggest that activation of JNK may play an important role in neuronal apoptosis and other physiological and pathological processes. The JNK Activity Immunoassay Kit utilizes a JNK-specific antibody to immunoprecipitate JNK from cell lysate. Activity of the JNK is then determined in a kinase reaction using recombinant c-Jun as substrate. Phosphorylation of the c-Jun can be analyzed by Western blot analysis using a phospho-c-Jun specific antibody. The kit specifically detects JNK, other kinase activity would not be detected.