A number of oligomers designed for Langmuir-Blodgett film deposition were investigated for their second-order non-linear optical properties. All the materials contain azo dye groups as their active chromophores. Values of the r coefficient up to 22 pm V-1 were measured for monolayers. Second harmonic generation was observed from both monolayers and multilayers. Although the second harmonic intensities generally increased with number of layers, the expected quadratic relationship was not satisfied. This indicates that chi(2)(-2omega; omega, omega) falls with increasing film thickness. Pockels’ effect experiments were used to elucidate this behaviour.