Purity >97 % by HPLC. L-JNK Peptide Inhibitor competitively blocks the interaction between JNK and c-Jun, thereby inhibiting the signaling events downstream of JNK, like c-Jun, ATF-2 and ELK1 phosphorylation. To convert JIP-1/IB-1 into cell permeable inhibitors of JNK (JNKI1) the minimal 20 amino acids inhibitory sequence of JIP-1/IB1 was covalently linked to the 10 amino acids recognized by TAT transporter. The L-JNKI1 is a potent inhibitor that is specific for JNK and can be used for in vitro applications.