The chemical background behind yellowing and pungent taste of Lactarius chrysorrheus and L scrobiculatus has been investigated. The intact fruit bodies originally contain a fatty acid ester of velutinal (i.e. compound 2b and 2a, respectively) as the only sesquiterpenoid When the fruit bodies are injured the esters are enzymatically converted into sesquiterpene furans, mono- and di-aldehydes, and lactones, which have been isolated and their structures elucidated These compounds have been submitted to conformational analysis by molecular mechanics and 1H NMR in order to make correct stereochemical assignments The pungent taste of the fruit bodies of both species is due to a new dialdehyde, chrysorrhedial (9), while a new triene-enolactone (8) is involved in the change of the colour