Langmuir-Blodgett (LB) films of a photosensitive polypeptide, prepared by introducing 31 mol% azobenzene moieties into the side chains of poly-L-lysine, have been deposited and studied using circular dichroism, infrared spectroscopy. X-ray reflection and surface plasmon resonance. The macroscopic structure of freshly prepared LB films consists of deformed polypeptide helices arranged in layers, with a layer thickness of about 2.0 nm. Infrared microscopy measurements in polarised light reveal some local order which decreases with increasing film thickness.