A fibre-optic sensor for the monitoring of hazardous exhaust gases is described. The sensor based on ultraviolet (UV) differential optical absorption spectroscopy (DOAS) was developed for the simultaneous monitoring of several exhaust gases from passenger cars. Experimental results describing the operation of this sensor with calibrated cylinder gases as well as in a full-size engine are presented. The sensor has been developed to operate within in exhaust environment and have low Susceptibility to interferences from other gases present. The lower limit of detection for the sensor was found to be 5 ppm for nitric oxide (NO), 1 ppm for both nitrogen dioxide (NO2) and sulphur dioxide (SO2) and response time was found to be 3.4 s. (C) 2007 Elsevier Ltd. All rights reserved.