β-Amanitin is an extremely toxic constituent of the mushroom, Amanita phalloides, that inhibits Rpb (eukaryotic RNA polymerase II) and eukaryotic RNA polymerase III. This toxin is synthesized as a proprotein, on ribosomes, 34 to 35 amino acids in length and then cleaved at specific proline residues by an enzyme belonging to the prolyl oligopeptidase (POP) subfamily. β-Amanitin shows remarkable binding affinity for eukaryotic RNA polymerase II, slightly binds to RNA polymerase III, and shows no activity on RNA polymerase I; it has been used to determine which types of RNA polymerase are present in a given sample. The toxin works by binding to the bridging helix of RNA polymerase II inhibiting the translocation of RNA and DNA needed to empty the site for the next round of synthesis; thereby slowing the rate of transcription by over 1000 fold.

β-Hexachlorcyclohexane is a byproduct of the production of insecticide lindane (γ-hexachlorocyclohexane). Technical grade hexachlorocyclohexane contains about 5-12% of technical grade hexachlorocyclohecane. Elevated levels of β-Hexachlorcyclohexane in blood was linked with risk of Alzheimer's disease and Parkinson's disease. β-Hexachlorcyclohexane is a xenoestrogen and promotes growth and invasiveness of breast tumor cell lines.

β-Zearalenol is a nonsteroidal estrogen of the resorcylic acid lactone group related to mycoestrogens found in Fusarium spp. β-Zearalenol is the β epimer of α-zearalenol and along with α-zearalenol is a major metabolite of zearalenone formed mainly in the liver but also to a lesser extent in the intestines during the first-pass metabolism. β-Zearalenol is about the same or slightly less potent as an estrogen relative to zearalenone. Contamination of grains by Fusarium species, notably maize, gives rise to high levels of zearalenol and is regarded as an important food quality issue for both human and animal health.