The present invention relates to a method and a device for detecting fumigants in air samples. The device can be designed for example as a portable analyzer 10 equipped with a stab probe 11 for sampling soil air. There are provided detection means 16 which, upon contact with the air sample, generate electrical signals which depend on the concentration of the fumigants to be detected in the air sample. In accordance with the invention, the detection means 16 comprise at least one mass-sensitive sensor, for example an array of quartz microbalances, which have suitable selective surface layers.