A microbial sensor for rapid measurement of the amount of biodegradable substances based on the salt-tolerant yeast Arxula adeninivorans LS3 has been developed especially for coastal and island regions. Our parameter, the so-called sensorBOD, that is available after only a few minutes, agrees with the 5-day value for the biochemical oxygen demand (BOD 5 ) very well. We have employed the Arxula sensor in the short-time estimation and supervision of the BOD of both domestic and industrial wastewater with high salinity. The novel sensor makes it possible to monitor the different types of wastewater rapidly without pretreatment, and it can be used for an active process control of sewage treatment works. Compared to a commercially available sensor, the novel sensor achieves better agreement between sensorBOD and BOD 5 measurements with salt containing samples.