Compounds observed in exhaled breath of cancer patients which are related to smoking behavior (GCMS). Only those measurements have been considered, which show at least 15% higher concentration in exhaled air than in indoor air. The relative proportions for observations with respect to smoker patients (red), ex-smoker patients (blue) and non-smoker patients (green) is shown. Nine compounds (blue) were identified by retention time and by spectral library identification. One compound, namely 1,3-cyclopentadiene was not commercially available and therefore only identified by spectral library match. Acetonitrile and toluene arise in almost every smokers' exhaled breath. p-Values computed according to the method of Agresti and Caffo  are smaller than 0.0001 with the exception of 2-methyl-1-butene and 1,4-pentadiene, where p < 0.05.