The response of a flame ionisation detector (FID) to cyanogen ((CN)2) and cyanogen chloride (CNCI) has been studied. The lower limits of detection for (CN)2and CNCl were 6×10−12moles and 2×10−11moles respectively. In a comparative study a thermal conductivity detector gave as its lower limit of detection for both (CN)2and CNCl 4×10−11moles. Both detectors showed excellent linearity over the range 0 to 10 micromoles. The ratio of the gradients of the FID calibrations (CN)2/CNCI were found to be approximately two suggesting the response depended on the cyani