Formaldehyde, at its dimedone adduct, formaldemethone, has been detected by thin-layer and high-performance liquid chromatography in extracts of all species tested of marine algae, macrofungi, lichens, bryophytes, pteridophytes, gymnosperms and angiosperms. The yields of formaldehyde recorded in this study varied from 30 microg/g to 4060 microg/g, fresh weight.