alpha,beta-Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline-promoted clays (Li+- and Cs+ -exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent-free procedure, alpha,beta-unsaturated nitriles have been produced in very high yields (97%) when the Cs+-saponite is used as catalyst. (C) 2004 Society of Chemical Industry.