14C- and 3H-labelled psilocin (4-hydroxy-N,N-dimethyl-tryptamine), the principal, active agent of hallucinogenic mushrooms, was synthesized from 2-methyl-3-nitrophenol via 4-benzyloxyindole. 14C-Labelled potassium cyanide was reacted with 4-benzyloxygramine (obtained from 4-benzyloxyindole) to give 14C-4-benzyloxy-3-indole acetic acid, an intermediate for 14C-psilocin synthesis. 3H-Labelled lithium aluminium hydride was used to react with 4-benzyloxy-3-indole-N,N-dimethyl-glyoxylamide (obtained from 4-benzyloxyindole) to give 3H-4-benzyloxy-psilocin which was debenzylated to form 3H-psilocin.