A discussion on on-line detection of organic products of incomplete combustion covers the use of MS with selective and soft (fragment free) ionization techniques; REMPI-TOFMS technique, which already used for on-line monitoring of PAH in flue gases of combustion processes; single-photon ionization with vacuum UV photons, a less selective but soft ionization method; monitoring of nearly simultaneous aromatic compounds (PAH) and other molecules, e.g., aldehydes or NO, using these two ionization methods; and first application results on waste incineration flue gas and automotive exhaust gas. Original is an abstract.