The odorous substance of Pseudomonas aeruginosa is proved to be identical with 2-Aminoacetophenone. Developed from paper chromatograms of the ether- and chloroform-extracts from culture material it is characterized by the blue fluorescence in ultra-violet light and the orangeyellow coloured Azomethine after spraying with p-dimethylaminobenzaldehyde. All strains of Pseudomonas aeruginosa being tested contained this substance although in different yields. Control determinations in strains of Pseudomonas fluorescens, Aeromonas hydrophila and Enterobacter aerogenes led to negative results.