GW788388 is a new TGF-beta type I receptor inhibitor with a much improved pharmacokinetic profile compared with SB431542. We studied its effect in vitro and found that it inhibited both the TGF-beta type I and type II receptor kinase activities, but not that of the related bone morphogenic protein type II receptor. Further, it blocked TGF-beta-induced Smad activation and target gene expression, while decreasing epithelial-mesenchymal transitions and fibrogenesis.