Pyrocatechol its sulfonic acid is often present in the urine of many mammals. Small amounts of catechol occur naturally in fruits and vegetables along with the enzyme polyphenol oxidase. Upon mixing the enzyme with the substrate and exposure to oxygen (as when a potato or apple is cut) the colorless catechol oxidizes to reddish-brown benzoquinone derivatives.

4-Methyl-6-Methoxycoumarin?is a natural product isolated from Eupatorium pauciflorum.

AtPep3 is a hormone-like peptide that plays a role in the salinity stress tolerance of plants.