GSK 3 Inhibitor IX (BIO) is a specific inhibitor of glycogen synthase kinase-3 (GSK-3), with IC50 of 5 nM for GSK-3α/β, shows > 16-fold selectivity over CDK5. GSK 3 Inhibitor IX interacts within the ATP binding pocket of these kinases, reduces β-catenin phosphorylation on a GSK-3-specific site in cellular models, closely mimicks Wnt signaling in Xenopus embryos. In human and mouse embryonic stem cells, GSK 3 Inhibitor IX (BIO) maintains the undifferentiated phenotype and sustains expression of the pluripotent state-specific transcription factors Oct-3/4, Rex-1 and Nanog. GSK 3 Inhibitor IX (BIO)-mediated Wnt activation is functionally reversible, as withdrawal of the compound leads to normal multidifferentiation programs in both human and mouse embryonic stem cells. GSK 3 Inhibitor IX (BIO) promotes proliferation in mammalian cardiomyocytes. GSK 3 Inhibitor IX (BIO) is also a pan-JAK inhibitor, with IC50 values of 0.03, 1.5, 8.0, 0.5 μM for TYK2, JAK1, JAK2 and JAK3, respectively. GSK 3 Inhibitor IX (BIO) selectively inhibits phosphorylation of STAT3 and induces apoptosis of human melanoma cells.