Bisindolylmaleimide IX (BIM IX) is a potent, cell-permeable inhibitor of protein kinase C (PKC) isoforms (IC50 = 5, 24, 14, 27, and 24 nM for PKC-α, PKC-βI, PKC-βII, PKC-γ, and PKC-ε, respectively). It is a poor inhibitor of protein kinase A (PKA, IC50 = 0.9 μM) and calcium/calmodulin kinase II (IC50 = 17 μM). BIM IX also inhibits glycogen synthase kinase 3 (IC50 = 6.8 nM).