A study was made of the interconversion of isomeric unsaturated C-4 nitriles (allyl cyanide, crotononitrile and methacrylonitrile) over strongly basic Na/NaY, and for comparison on neutral NaY and acidic CaY catalysts at 623 K. Pulse experiments indicated the facile transformation of allyl cyanide to crotononitrile and the low reactivities of crotononitrile and methacrylonitrile. FTIR studies of the adsorbed molecules revealed the possible involvement of anionic intermediates.