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.

Lauroyl-L-carnitine (chloride) (Lauroyl-L-carnitine Hydrochloride), an acylcarnitine and surfactant, has been used to permeate porcine intestinal cells to deliver the polar fluorescent probe fluorescent yellow.

Aristolone has potential anti-cancer activity.