Langmuir monolayers of an amphiphilic ketone 1 have been studied on pure water and on aqueous subphases containing sodium borohydride. Changes in the compression isotherm and in the monolayer morphology were observed when the concentration of NaBH4 or the delay between spreading and compression was increased. These modifications were specific to NaBH4 and suggested that a chemical reaction is taking place along the monolayer. Modifications in the IR spectrum of the corresponding Langmuir-Blodgett film confirmed the reduction of the ketone group of 1 when spread on aqueous subphases of sodium borohydride. Analysis of the compression isotherms demonstrated that this reaction occurred for all surface pressures and therefore indicated that the ketone group of 1 is accessible to the borohydride whatever the compression state of the monolayer. (c) 2005 Elsevier Inc. All rights reserved.