Analysis of ten fruit bodies of Inocybe aeruginascens Babos revealed a content of the indole derivative aeruginascin which was in the same order of magnitude as the amounts of psilocybin or baeocystin. There was a correlation between the content of psilocybin, baeocystin and aeruginascin. Aeruginascin seems to modify the pharmacological action of psilocybin to give an always euphoric mood during ingestion of the mushrooms.