Polymeric Langmuir-Blodgett films incorporating a sulphonyl-substituted azobenzene chromophore have been studied by second harmonic generation. These films are more stable to light and more transparent than alternatives based on hemicyanine and other azo dyes that have been used previously. The initial 100 nm of polymeric LB film, nearest the substrate, exhibits a nonlinear susceptibility of chi(pp)((2)) = 6.3 pm V-1 and a chromophore nonlinear vector susceptibility of magnitude beta = 46 x 10(-50) C-2 m(-3) V-2. A loss of performance is observed for molecular layers a distance greater than 100 nm from the substrate, which is reflected in a reduced but uniform nonlinearity in the layers deposited later in the sample fabrication process.