Floating monolayers as well as Langmuir-Blodgett (LB) films of poly(isocyanide)s containing NLO-active side chains appear to be capable of generating second-harmonic light. Spin-coated films and cast films of these polymers do not shown this behavior. These results indicate that the NLO activity of the LB films originates from the orientation of the side chains obtained at-the air-water interface. In the case of poly(isocyanide)s with relatively hydrophobic side chains the second-harmonic intensities generated from the LB films are small, probably because the dins are of the Y-type. Poly(isocyanide)s with more hydrophilic side chains form LB films which are Z-type. These Rims show stable second-harmonic generation without the need of poling with high electrical fields at high temperatures.