Phorbol 12,13-dibutyrate (PDBu; Phorbol dibutyrate) is a phorbol ester acting as a PKC activator and a potent skin tumor promoter. It is one of the constituents of croton oil. As an activator of protein kinase C, it is a weak tumor promoter compared to 12-O-tetradecanoylphorbol-13-acetate.