Abstract: A microsensor for detecting corrosive media acting on a bulk metallic material when mounted in situ adjacent a location in the bulk metallic material. The microsensor includes a plurality of corrosion sensors (4A, 4B, 4C) exposed to the corrosive media, each having corrosive tracks formed from a patterned conductive thin film. The different sensors have different characteristics, such as track width, track thickness, track composition, surface type, sensor type, etc. so as to provide the sensors with different sensitivities, corrosion indications and lifetime characteristics. Such microsensor arrangements provide improved corrosion detection at high degrees of miniaturisation.