The use of a hallucinogenic mushroom, PSILOCYBE SEMILANCEATA, has been occasionally reported in Finland, where the species is widely distributed. We have determined, by HPLC, the content of psilocybin and psilocin in P. SEMILANCEATA samples collected from different parts of Finland; the psilocybin content was found to be high (0.62-2.37%, mean 1.42% of dry weight), some samples also contained low concentrations (0.01-0.02% dry weight) of psilocin.