Gas chromatography (GC), mass spectrometry (MS), GC/MS technique and standardized methods have been used to investigate harmful chemicals produced during laser treatment of tissue and to find relations between the emitted molecules and interaction processes. It has been found that the emission of carbon monoxide is strongly connected with carbonization. Hydrocyanic acid is well suited to get information on processes, characterizing laser tissue interaction, e.g., plasma behavior. From results obtained by variation of the reaction gas atmosphere (helium, nitrogen oxygen, air) it becomes clear that two processes must be taken into account, oxidation (combustion) and the preferred formation of compounds characterized by the cyano group. It is possible to reduce the amount of emitted hydrocyanic acid drastically working in an oxygen atmosphere. The typical substances arising during laser tissue interaction were compared with the emission obtained by laser treatment of fiber-reinforced plastics, pointing out that the high temperature region (plasma torch) is an important source of the emitted substances.