Abstract: The invention relates to an instrument for chemi- or bioluminescent analysis of the concentration of a constituent of a sample gas (G.sub.1) which in a reaction chamber (C) reacts with a liquid reagent (R.sub.1) in a luminescent manner. The liquid reagent (R.sub.1) is ejected into the reaction chamber (C) by ejection means. The sample gas (G.sub.1) can be used as propellant in the ejection means (E) sucking the liquid reagent (R.sub.1) into the propellant and as an aerosol be sprayed into the reaction chamber. Carefully mixed with the sample gas, it generates chemiluminescent radiation (L.sub.1, L.sub.2) in the field of view of a photodetector (D). The propellant (G.sub.1) can also be prepared so that either heating or cooling occurs on expansion in the reaction chamber (C). By providing walls of the reaction chamber with reflecting layers, the main portion of the luminescent radiation reaches the detector (D).