The blue-staining Psilocybe and Panaeolus species get their psychoactive properties from the high levels of psilocin and psilocybin that they contain. (The blue staining is directly correlated with psilocin content, as it results from the oxidation by air of an unidentified compound that is produced by the degeneration of psilocin.)

Many books on hallucinogenic mushrooms suggest a simple test for psilocybian species which involves breaking the flesh of the specimen and waiting about 30 minutes for a blueing reaction to take place. The blueing is due to the oxidization of indole based substances in the fungus. Although it is true that most of the psilocybin-bearing mushrooms will respond positively to this test, other species may do the same. The poisonous Eastwood Boletus blues upon exposure of the inner tissues to oxygen as well as does any psilocybin mushroom. Another test which is often given in mushroom manuals is treating the exposed tissues with Metol, a chemical used in photo developers. It hastens the blueing of psilocybin mushrooms, and supposedly one can do a blueing test with it in a few minutes that would otherwise take 30 minutes or more. Any mushroom, however, which contains indolic substances of any sort will respond positively to this test. Since indole-based amino acids such as tryptophan are found in most living organisms this test is rather useless.