Abstract: A method of detection of a volatile compound in a gaseous atmosphere comprises irradiating a semiconducting metal oxide material with ultraviolet light, exposing the irradiated material to the gaseous atmosphere and determining the presence of any volatile compound in the atmosphere by monitoring a change in electrical conductivity of the material. The method can detect non-polar organic compounds as well as polar compounds. Zinc oxide particles in the nanometre size range are preferred. The method may be used for medical diagnosis or for environment monitoring purposes.