Fiber laser intracavity spectroscopy (FLICAS) with Er-doped fiber laser has been applied for the first in situ detection of ammonia and hydrogen cyanide in a low pressure (30 Torr) stoichiometric methane/nitrogen/oxygen flame doped with 0.13-1.36% of NH3. High resolution spectra of NH3 and HCN have been recorded in the range of 1.5 gin (6440-6540 cm(-1)). The minimum detectable concentration of HCN and NH3 at a laser pulse duration of 8 mu s and room temperature is 1 x 10(13) molecule/cm(3). The method can be used for in situ detection of many other molecules in the hostile combustion environment. (c) 2006 Elsevier B.V. All rights reserved.