4-Phenylbut-1-ene isomerizes to a mixture of cis- and trans-1-phenylbut-2-ene and trans-1-phenylbut-1-ene in the presence of bis(benzonitrile)dichloropalladium(11). The products are not formed entirely in consecutive reactions but direct conversion of 4-phenylbut-1-ene into trans-1-phenylbut-1-ene occurs extensively. Similarities are observed in the kinetics with those observed previously for allylbenzene. The isomerization of 1-phenylbut-2-ene to 1-phenylbut-1-ene is comparatively slow in spite of conjugation between the aromatic ring and the double bond in the side-chain within the latter compound. The rate-controlling step in the isomerization of 1-phenylbut-2-ene is believed to be an olefin displacement reaction, but an induction period renders the conclusions with regard to the kinetics of the initial isomerization of 4-phenylbut-1-ene less certain.