A 83-01 is a potent activing receptor-like kinase inhibitor (ALK4 IC50 45nM, ALK5 IC50 12nM, ALK7 IC50 7.5nM). It is a more potent inhibitor of ALK5 than SB 431542 and is reported to inhibit Smad signaling and epithelial-to-mesenchymal transition by transforming growth factor-beta. However, A 83-01 had little or no effect on bone morphogenetic protein type I receptors, p38 mitogen-activated protein kinase, or extracellular regulated kinase. It is used to inhibit differentiation in iPSCs and maintain in vitro cellular self-renewal.